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/handler/user_handler.go

@@ -30,7 +30,6 @@ type ChangePasswordRequest struct {
 // UpdateProfileRequest represents the update profile request payload
 type UpdateProfileRequest struct {
 	Username *string `json:"username"`
-	Wechat   *string `json:"wechat"`
 }
 
 // GetProfile handles getting user profile
@@ -99,7 +98,6 @@ func (h *UserHandler) UpdateProfile(c *gin.Context) {
 
 	svcReq := service.UpdateProfileRequest{
 		Username: req.Username,
-		Wechat:   req.Wechat,
 	}
 	updatedUser, err := h.userService.UpdateProfile(c.Request.Context(), subject.UserID, svcReq)
 	if err != nil {