feat(security): 启动时自动迁移并持久化JWT密钥

- 新增 security_secrets 表及 Ent schema 用于存储系统级密钥
- 启动阶段支持无 jwt.secret 配置并在数据库中自动生成持久化
- 在 Ent 初始化后补齐密钥并执行完整配置校验
- 增加并发与异常分支单元测试，覆盖密钥引导核心路径

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/ent/securitysecret.go

@@ -0,0 +1,139 @@
+// Code generated by ent, DO NOT EDIT.
+
+package ent
+
+import (
+	"fmt"
+	"strings"
+	"time"
+
+	"entgo.io/ent"
+	"entgo.io/ent/dialect/sql"
+	"github.com/Wei-Shaw/sub2api/ent/securitysecret"
+)
+
+// SecuritySecret is the model entity for the SecuritySecret schema.
+type SecuritySecret struct {
+	config `json:"-"`
+	// ID of the ent.
+	ID int64 `json:"id,omitempty"`
+	// CreatedAt holds the value of the "created_at" field.
+	CreatedAt time.Time `json:"created_at,omitempty"`
+	// UpdatedAt holds the value of the "updated_at" field.
+	UpdatedAt time.Time `json:"updated_at,omitempty"`
+	// Key holds the value of the "key" field.
+	Key string `json:"key,omitempty"`
+	// Value holds the value of the "value" field.
+	Value        string `json:"value,omitempty"`
+	selectValues sql.SelectValues
+}
+
+// scanValues returns the types for scanning values from sql.Rows.
+func (*SecuritySecret) scanValues(columns []string) ([]any, error) {
+	values := make([]any, len(columns))
+	for i := range columns {
+		switch columns[i] {
+		case securitysecret.FieldID:
+			values[i] = new(sql.NullInt64)
+		case securitysecret.FieldKey, securitysecret.FieldValue:
+			values[i] = new(sql.NullString)
+		case securitysecret.FieldCreatedAt, securitysecret.FieldUpdatedAt:
+			values[i] = new(sql.NullTime)
+		default:
+			values[i] = new(sql.UnknownType)
+		}
+	}
+	return values, nil
+}
+
+// assignValues assigns the values that were returned from sql.Rows (after scanning)
+// to the SecuritySecret fields.
+func (_m *SecuritySecret) assignValues(columns []string, values []any) error {
+	if m, n := len(values), len(columns); m < n {
+		return fmt.Errorf("mismatch number of scan values: %d != %d", m, n)
+	}
+	for i := range columns {
+		switch columns[i] {
+		case securitysecret.FieldID:
+			value, ok := values[i].(*sql.NullInt64)
+			if !ok {
+				return fmt.Errorf("unexpected type %T for field id", value)
+			}
+			_m.ID = int64(value.Int64)
+		case securitysecret.FieldCreatedAt:
+			if value, ok := values[i].(*sql.NullTime); !ok {
+				return fmt.Errorf("unexpected type %T for field created_at", values[i])
+			} else if value.Valid {
+				_m.CreatedAt = value.Time
+			}
+		case securitysecret.FieldUpdatedAt:
+			if value, ok := values[i].(*sql.NullTime); !ok {
+				return fmt.Errorf("unexpected type %T for field updated_at", values[i])
+			} else if value.Valid {
+				_m.UpdatedAt = value.Time
+			}
+		case securitysecret.FieldKey:
+			if value, ok := values[i].(*sql.NullString); !ok {
+				return fmt.Errorf("unexpected type %T for field key", values[i])
+			} else if value.Valid {
+				_m.Key = value.String
+			}
+		case securitysecret.FieldValue:
+			if value, ok := values[i].(*sql.NullString); !ok {
+				return fmt.Errorf("unexpected type %T for field value", values[i])
+			} else if value.Valid {
+				_m.Value = value.String
+			}
+		default:
+			_m.selectValues.Set(columns[i], values[i])
+		}
+	}
+	return nil
+}
+
+// GetValue returns the ent.Value that was dynamically selected and assigned to the SecuritySecret.
+// This includes values selected through modifiers, order, etc.
+func (_m *SecuritySecret) GetValue(name string) (ent.Value, error) {
+	return _m.selectValues.Get(name)
+}
+
+// Update returns a builder for updating this SecuritySecret.
+// Note that you need to call SecuritySecret.Unwrap() before calling this method if this SecuritySecret
+// was returned from a transaction, and the transaction was committed or rolled back.
+func (_m *SecuritySecret) Update() *SecuritySecretUpdateOne {
+	return NewSecuritySecretClient(_m.config).UpdateOne(_m)
+}
+
+// Unwrap unwraps the SecuritySecret entity that was returned from a transaction after it was closed,
+// so that all future queries will be executed through the driver which created the transaction.
+func (_m *SecuritySecret) Unwrap() *SecuritySecret {
+	_tx, ok := _m.config.driver.(*txDriver)
+	if !ok {
+		panic("ent: SecuritySecret is not a transactional entity")
+	}
+	_m.config.driver = _tx.drv
+	return _m
+}
+
+// String implements the fmt.Stringer.
+func (_m *SecuritySecret) String() string {
+	var builder strings.Builder
+	builder.WriteString("SecuritySecret(")
+	builder.WriteString(fmt.Sprintf("id=%v, ", _m.ID))
+	builder.WriteString("created_at=")
+	builder.WriteString(_m.CreatedAt.Format(time.ANSIC))
+	builder.WriteString(", ")
+	builder.WriteString("updated_at=")
+	builder.WriteString(_m.UpdatedAt.Format(time.ANSIC))
+	builder.WriteString(", ")
+	builder.WriteString("key=")
+	builder.WriteString(_m.Key)
+	builder.WriteString(", ")
+	builder.WriteString("value=")
+	builder.WriteString(_m.Value)
+	builder.WriteByte(')')
+	return builder.String()
+}
+
+// SecuritySecrets is a parsable slice of SecuritySecret.
+type SecuritySecrets []*SecuritySecret