refactor: migrate wechat to user attributes and enhance users list

Migrate the hardcoded wechat field to the new extensible user
attributes system and improve the users management UI.

Migration:
- Add migration 019 to move wechat data to user_attribute_values
- Remove wechat field from User entity, DTOs, and API contracts
- Clean up wechat-related code from backend and frontend

UsersView enhancements:
- Add text labels to action buttons (Filter Settings, Column Settings,
  Attributes Config) for better UX
- Change status column to show colored dot + Chinese text instead of
  English text
- Add dynamic attribute columns support with batch loading
- Add column visibility settings with localStorage persistence
- Add filter settings modal for search and filter preferences
- Update i18n translations

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

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

backend/internal/service/user_service.go

@@ -14,6 +14,14 @@ var (
 	ErrInsufficientPerms = infraerrors.Forbidden("INSUFFICIENT_PERMISSIONS", "insufficient permissions")
 )
 
+// UserListFilters contains all filter options for listing users
+type UserListFilters struct {
+	Status     string            // User status filter
+	Role       string            // User role filter
+	Search     string            // Search in email, username
+	Attributes map[int64]string  // Custom attribute filters: attributeID -> value
+}
+
 type UserRepository interface {
 	Create(ctx context.Context, user *User) error
 	GetByID(ctx context.Context, id int64) (*User, error)
@@ -23,7 +31,7 @@ type UserRepository interface {
 	Delete(ctx context.Context, id int64) error
 
 	List(ctx context.Context, params pagination.PaginationParams) ([]User, *pagination.PaginationResult, error)
-	ListWithFilters(ctx context.Context, params pagination.PaginationParams, status, role, search string) ([]User, *pagination.PaginationResult, error)
+	ListWithFilters(ctx context.Context, params pagination.PaginationParams, filters UserListFilters) ([]User, *pagination.PaginationResult, error)
 
 	UpdateBalance(ctx context.Context, id int64, amount float64) error
 	DeductBalance(ctx context.Context, id int64, amount float64) error
@@ -36,7 +44,6 @@ type UserRepository interface {
 type UpdateProfileRequest struct {
 	Email       *string `json:"email"`
 	Username    *string `json:"username"`
-	Wechat      *string `json:"wechat"`
 	Concurrency *int    `json:"concurrency"`
 }
 
@@ -100,10 +107,6 @@ func (s *UserService) UpdateProfile(ctx context.Context, userID int64, req Updat
 		user.Username = *req.Username
 	}
 
-	if req.Wechat != nil {
-		user.Wechat = *req.Wechat
-	}
-
 	if req.Concurrency != nil {
 		user.Concurrency = *req.Concurrency
 	}