feat(backend): add user custom attributes system

Add a flexible user attribute system that allows admins to define
custom fields for users (text, textarea, number, email, url, date,
select, multi_select types).

- Add Ent schemas for UserAttributeDefinition and UserAttributeValue
- Add service layer with validation logic
- Add repository layer with batch operations support
- Add admin API endpoints for CRUD and reorder operations
- Add batch API for loading attribute values for multiple users
- Add database migration (018_user_attributes.sql)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/ent/userattributevalue/userattributevalue.go

@@ -0,0 +1,139 @@
+// Code generated by ent, DO NOT EDIT.
+
+package userattributevalue
+
+import (
+	"time"
+
+	"entgo.io/ent/dialect/sql"
+	"entgo.io/ent/dialect/sql/sqlgraph"
+)
+
+const (
+	// Label holds the string label denoting the userattributevalue type in the database.
+	Label = "user_attribute_value"
+	// 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"
+	// FieldUserID holds the string denoting the user_id field in the database.
+	FieldUserID = "user_id"
+	// FieldAttributeID holds the string denoting the attribute_id field in the database.
+	FieldAttributeID = "attribute_id"
+	// FieldValue holds the string denoting the value field in the database.
+	FieldValue = "value"
+	// EdgeUser holds the string denoting the user edge name in mutations.
+	EdgeUser = "user"
+	// EdgeDefinition holds the string denoting the definition edge name in mutations.
+	EdgeDefinition = "definition"
+	// Table holds the table name of the userattributevalue in the database.
+	Table = "user_attribute_values"
+	// UserTable is the table that holds the user relation/edge.
+	UserTable = "user_attribute_values"
+	// UserInverseTable is the table name for the User entity.
+	// It exists in this package in order to avoid circular dependency with the "user" package.
+	UserInverseTable = "users"
+	// UserColumn is the table column denoting the user relation/edge.
+	UserColumn = "user_id"
+	// DefinitionTable is the table that holds the definition relation/edge.
+	DefinitionTable = "user_attribute_values"
+	// DefinitionInverseTable is the table name for the UserAttributeDefinition entity.
+	// It exists in this package in order to avoid circular dependency with the "userattributedefinition" package.
+	DefinitionInverseTable = "user_attribute_definitions"
+	// DefinitionColumn is the table column denoting the definition relation/edge.
+	DefinitionColumn = "attribute_id"
+)
+
+// Columns holds all SQL columns for userattributevalue fields.
+var Columns = []string{
+	FieldID,
+	FieldCreatedAt,
+	FieldUpdatedAt,
+	FieldUserID,
+	FieldAttributeID,
+	FieldValue,
+}
+
+// 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
+}
+
+var (
+	// 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
+	// DefaultValue holds the default value on creation for the "value" field.
+	DefaultValue string
+)
+
+// OrderOption defines the ordering options for the UserAttributeValue 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()
+}
+
+// ByUserID orders the results by the user_id field.
+func ByUserID(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldUserID, opts...).ToFunc()
+}
+
+// ByAttributeID orders the results by the attribute_id field.
+func ByAttributeID(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldAttributeID, opts...).ToFunc()
+}
+
+// ByValue orders the results by the value field.
+func ByValue(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldValue, opts...).ToFunc()
+}
+
+// ByUserField orders the results by user field.
+func ByUserField(field string, opts ...sql.OrderTermOption) OrderOption {
+	return func(s *sql.Selector) {
+		sqlgraph.OrderByNeighborTerms(s, newUserStep(), sql.OrderByField(field, opts...))
+	}
+}
+
+// ByDefinitionField orders the results by definition field.
+func ByDefinitionField(field string, opts ...sql.OrderTermOption) OrderOption {
+	return func(s *sql.Selector) {
+		sqlgraph.OrderByNeighborTerms(s, newDefinitionStep(), sql.OrderByField(field, opts...))
+	}
+}
+func newUserStep() *sqlgraph.Step {
+	return sqlgraph.NewStep(
+		sqlgraph.From(Table, FieldID),
+		sqlgraph.To(UserInverseTable, FieldID),
+		sqlgraph.Edge(sqlgraph.M2O, true, UserTable, UserColumn),
+	)
+}
+func newDefinitionStep() *sqlgraph.Step {
+	return sqlgraph.NewStep(
+		sqlgraph.From(Table, FieldID),
+		sqlgraph.To(DefinitionInverseTable, FieldID),
+		sqlgraph.Edge(sqlgraph.M2O, true, DefinitionTable, DefinitionColumn),
+	)
+}