refactor(数据库): 迁移持久层到 Ent 并清理 GORM

将仓储层/基础设施改为 Ent + 原生 SQL 执行路径，并移除 AutoMigrate 与 GORM 依赖。
重构内容包括：
- 仓储层改用 Ent/SQL（含 usage_log/account 等复杂查询），统一错误映射
- 基础设施与 setup 初始化切换为 Ent + SQL migrations
- 集成测试与 fixtures 迁移到 Ent 事务模型
- 清理遗留 GORM 模型/依赖，补充迁移与文档说明
- 增加根目录 Makefile 便于前后端编译

测试：
- go test -tags unit ./...
- go test -tags integration ./...

backend/ent/account/account.go

@@ -0,0 +1,303 @@
+// Code generated by ent, DO NOT EDIT.
+
+package account
+
+import (
+	"time"
+
+	"entgo.io/ent"
+	"entgo.io/ent/dialect/sql"
+	"entgo.io/ent/dialect/sql/sqlgraph"
+)
+
+const (
+	// Label holds the string label denoting the account type in the database.
+	Label = "account"
+	// FieldID holds the string denoting the id field in the database.
+	FieldID = "id"
+	// FieldCreatedAt holds the string denoting the created_at field in the database.
+	FieldCreatedAt = "created_at"
+	// FieldUpdatedAt holds the string denoting the updated_at field in the database.
+	FieldUpdatedAt = "updated_at"
+	// FieldDeletedAt holds the string denoting the deleted_at field in the database.
+	FieldDeletedAt = "deleted_at"
+	// FieldName holds the string denoting the name field in the database.
+	FieldName = "name"
+	// FieldPlatform holds the string denoting the platform field in the database.
+	FieldPlatform = "platform"
+	// FieldType holds the string denoting the type field in the database.
+	FieldType = "type"
+	// FieldCredentials holds the string denoting the credentials field in the database.
+	FieldCredentials = "credentials"
+	// FieldExtra holds the string denoting the extra field in the database.
+	FieldExtra = "extra"
+	// FieldProxyID holds the string denoting the proxy_id field in the database.
+	FieldProxyID = "proxy_id"
+	// FieldConcurrency holds the string denoting the concurrency field in the database.
+	FieldConcurrency = "concurrency"
+	// FieldPriority holds the string denoting the priority field in the database.
+	FieldPriority = "priority"
+	// FieldStatus holds the string denoting the status field in the database.
+	FieldStatus = "status"
+	// FieldErrorMessage holds the string denoting the error_message field in the database.
+	FieldErrorMessage = "error_message"
+	// FieldLastUsedAt holds the string denoting the last_used_at field in the database.
+	FieldLastUsedAt = "last_used_at"
+	// FieldSchedulable holds the string denoting the schedulable field in the database.
+	FieldSchedulable = "schedulable"
+	// FieldRateLimitedAt holds the string denoting the rate_limited_at field in the database.
+	FieldRateLimitedAt = "rate_limited_at"
+	// FieldRateLimitResetAt holds the string denoting the rate_limit_reset_at field in the database.
+	FieldRateLimitResetAt = "rate_limit_reset_at"
+	// FieldOverloadUntil holds the string denoting the overload_until field in the database.
+	FieldOverloadUntil = "overload_until"
+	// FieldSessionWindowStart holds the string denoting the session_window_start field in the database.
+	FieldSessionWindowStart = "session_window_start"
+	// FieldSessionWindowEnd holds the string denoting the session_window_end field in the database.
+	FieldSessionWindowEnd = "session_window_end"
+	// FieldSessionWindowStatus holds the string denoting the session_window_status field in the database.
+	FieldSessionWindowStatus = "session_window_status"
+	// EdgeGroups holds the string denoting the groups edge name in mutations.
+	EdgeGroups = "groups"
+	// EdgeAccountGroups holds the string denoting the account_groups edge name in mutations.
+	EdgeAccountGroups = "account_groups"
+	// Table holds the table name of the account in the database.
+	Table = "accounts"
+	// GroupsTable is the table that holds the groups relation/edge. The primary key declared below.
+	GroupsTable = "account_groups"
+	// GroupsInverseTable is the table name for the Group entity.
+	// It exists in this package in order to avoid circular dependency with the "group" package.
+	GroupsInverseTable = "groups"
+	// AccountGroupsTable is the table that holds the account_groups relation/edge.
+	AccountGroupsTable = "account_groups"
+	// AccountGroupsInverseTable is the table name for the AccountGroup entity.
+	// It exists in this package in order to avoid circular dependency with the "accountgroup" package.
+	AccountGroupsInverseTable = "account_groups"
+	// AccountGroupsColumn is the table column denoting the account_groups relation/edge.
+	AccountGroupsColumn = "account_id"
+)
+
+// Columns holds all SQL columns for account fields.
+var Columns = []string{
+	FieldID,
+	FieldCreatedAt,
+	FieldUpdatedAt,
+	FieldDeletedAt,
+	FieldName,
+	FieldPlatform,
+	FieldType,
+	FieldCredentials,
+	FieldExtra,
+	FieldProxyID,
+	FieldConcurrency,
+	FieldPriority,
+	FieldStatus,
+	FieldErrorMessage,
+	FieldLastUsedAt,
+	FieldSchedulable,
+	FieldRateLimitedAt,
+	FieldRateLimitResetAt,
+	FieldOverloadUntil,
+	FieldSessionWindowStart,
+	FieldSessionWindowEnd,
+	FieldSessionWindowStatus,
+}
+
+var (
+	// GroupsPrimaryKey and GroupsColumn2 are the table columns denoting the
+	// primary key for the groups relation (M2M).
+	GroupsPrimaryKey = []string{"account_id", "group_id"}
+)
+
+// ValidColumn reports if the column name is valid (part of the table columns).
+func ValidColumn(column string) bool {
+	for i := range Columns {
+		if column == Columns[i] {
+			return true
+		}
+	}
+	return false
+}
+
+// Note that the variables below are initialized by the runtime
+// package on the initialization of the application. Therefore,
+// it should be imported in the main as follows:
+//
+//	import _ "github.com/Wei-Shaw/sub2api/ent/runtime"
+var (
+	Hooks        [1]ent.Hook
+	Interceptors [1]ent.Interceptor
+	// DefaultCreatedAt holds the default value on creation for the "created_at" field.
+	DefaultCreatedAt func() time.Time
+	// DefaultUpdatedAt holds the default value on creation for the "updated_at" field.
+	DefaultUpdatedAt func() time.Time
+	// UpdateDefaultUpdatedAt holds the default value on update for the "updated_at" field.
+	UpdateDefaultUpdatedAt func() time.Time
+	// NameValidator is a validator for the "name" field. It is called by the builders before save.
+	NameValidator func(string) error
+	// PlatformValidator is a validator for the "platform" field. It is called by the builders before save.
+	PlatformValidator func(string) error
+	// TypeValidator is a validator for the "type" field. It is called by the builders before save.
+	TypeValidator func(string) error
+	// DefaultCredentials holds the default value on creation for the "credentials" field.
+	DefaultCredentials func() map[string]interface{}
+	// DefaultExtra holds the default value on creation for the "extra" field.
+	DefaultExtra func() map[string]interface{}
+	// DefaultConcurrency holds the default value on creation for the "concurrency" field.
+	DefaultConcurrency int
+	// DefaultPriority holds the default value on creation for the "priority" field.
+	DefaultPriority int
+	// DefaultStatus holds the default value on creation for the "status" field.
+	DefaultStatus string
+	// StatusValidator is a validator for the "status" field. It is called by the builders before save.
+	StatusValidator func(string) error
+	// DefaultSchedulable holds the default value on creation for the "schedulable" field.
+	DefaultSchedulable bool
+	// SessionWindowStatusValidator is a validator for the "session_window_status" field. It is called by the builders before save.
+	SessionWindowStatusValidator func(string) error
+)
+
+// OrderOption defines the ordering options for the Account queries.
+type OrderOption func(*sql.Selector)
+
+// ByID orders the results by the id field.
+func ByID(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldID, opts...).ToFunc()
+}
+
+// ByCreatedAt orders the results by the created_at field.
+func ByCreatedAt(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldCreatedAt, opts...).ToFunc()
+}
+
+// ByUpdatedAt orders the results by the updated_at field.
+func ByUpdatedAt(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldUpdatedAt, opts...).ToFunc()
+}
+
+// ByDeletedAt orders the results by the deleted_at field.
+func ByDeletedAt(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldDeletedAt, opts...).ToFunc()
+}
+
+// ByName orders the results by the name field.
+func ByName(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldName, opts...).ToFunc()
+}
+
+// ByPlatform orders the results by the platform field.
+func ByPlatform(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldPlatform, opts...).ToFunc()
+}
+
+// ByType orders the results by the type field.
+func ByType(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldType, opts...).ToFunc()
+}
+
+// ByProxyID orders the results by the proxy_id field.
+func ByProxyID(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldProxyID, opts...).ToFunc()
+}
+
+// ByConcurrency orders the results by the concurrency field.
+func ByConcurrency(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldConcurrency, opts...).ToFunc()
+}
+
+// ByPriority orders the results by the priority field.
+func ByPriority(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldPriority, opts...).ToFunc()
+}
+
+// ByStatus orders the results by the status field.
+func ByStatus(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldStatus, opts...).ToFunc()
+}
+
+// ByErrorMessage orders the results by the error_message field.
+func ByErrorMessage(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldErrorMessage, opts...).ToFunc()
+}
+
+// ByLastUsedAt orders the results by the last_used_at field.
+func ByLastUsedAt(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldLastUsedAt, opts...).ToFunc()
+}
+
+// BySchedulable orders the results by the schedulable field.
+func BySchedulable(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldSchedulable, opts...).ToFunc()
+}
+
+// ByRateLimitedAt orders the results by the rate_limited_at field.
+func ByRateLimitedAt(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldRateLimitedAt, opts...).ToFunc()
+}
+
+// ByRateLimitResetAt orders the results by the rate_limit_reset_at field.
+func ByRateLimitResetAt(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldRateLimitResetAt, opts...).ToFunc()
+}
+
+// ByOverloadUntil orders the results by the overload_until field.
+func ByOverloadUntil(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldOverloadUntil, opts...).ToFunc()
+}
+
+// BySessionWindowStart orders the results by the session_window_start field.
+func BySessionWindowStart(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldSessionWindowStart, opts...).ToFunc()
+}
+
+// BySessionWindowEnd orders the results by the session_window_end field.
+func BySessionWindowEnd(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldSessionWindowEnd, opts...).ToFunc()
+}
+
+// BySessionWindowStatus orders the results by the session_window_status field.
+func BySessionWindowStatus(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldSessionWindowStatus, opts...).ToFunc()
+}
+
+// ByGroupsCount orders the results by groups count.
+func ByGroupsCount(opts ...sql.OrderTermOption) OrderOption {
+	return func(s *sql.Selector) {
+		sqlgraph.OrderByNeighborsCount(s, newGroupsStep(), opts...)
+	}
+}
+
+// ByGroups orders the results by groups terms.
+func ByGroups(term sql.OrderTerm, terms ...sql.OrderTerm) OrderOption {
+	return func(s *sql.Selector) {
+		sqlgraph.OrderByNeighborTerms(s, newGroupsStep(), append([]sql.OrderTerm{term}, terms...)...)
+	}
+}
+
+// ByAccountGroupsCount orders the results by account_groups count.
+func ByAccountGroupsCount(opts ...sql.OrderTermOption) OrderOption {
+	return func(s *sql.Selector) {
+		sqlgraph.OrderByNeighborsCount(s, newAccountGroupsStep(), opts...)
+	}
+}
+
+// ByAccountGroups orders the results by account_groups terms.
+func ByAccountGroups(term sql.OrderTerm, terms ...sql.OrderTerm) OrderOption {
+	return func(s *sql.Selector) {
+		sqlgraph.OrderByNeighborTerms(s, newAccountGroupsStep(), append([]sql.OrderTerm{term}, terms...)...)
+	}
+}
+func newGroupsStep() *sqlgraph.Step {
+	return sqlgraph.NewStep(
+		sqlgraph.From(Table, FieldID),
+		sqlgraph.To(GroupsInverseTable, FieldID),
+		sqlgraph.Edge(sqlgraph.M2M, false, GroupsTable, GroupsPrimaryKey...),
+	)
+}
+func newAccountGroupsStep() *sqlgraph.Step {
+	return sqlgraph.NewStep(
+		sqlgraph.From(Table, FieldID),
+		sqlgraph.To(AccountGroupsInverseTable, AccountGroupsColumn),
+		sqlgraph.Edge(sqlgraph.O2M, true, AccountGroupsTable, AccountGroupsColumn),
+	)
+}