feat(marketing): user profile update, ad placement management, logo limits

- Add PUT /auth/profile endpoint for nickname and avatar updates
- Add ad_placements table and CRUD admin API for managing ad units
- Add GET /marketing/ad-config public API for mini-program to fetch ad config
- Reduce logo limit from 10 to 3 per user, add 2MB file size validation

Made-with: Cursor

internal/marketing/service/user_logo_service.go

@@ -7,9 +7,13 @@ import (
 	"wx_service/internal/marketing/repository"
 )
 
-const MaxLogosPerUser = 10
+const MaxLogosPerUser = 3
+const MaxLogoFileSize = 2 * 1024 * 1024 // 2MB
 
-var ErrLogoLimitReached = errors.New("Logo 数量已达上限")
+var (
+	ErrLogoLimitReached = errors.New("Logo 数量已达上限")
+	ErrLogoTooLarge     = errors.New("Logo 文件不能超过 2MB")
+)
 
 type UserLogoService struct {
 	repo *repository.UserLogoRepository
@@ -26,6 +30,10 @@ type SaveLogoRequest struct {
 }
 
 func (s *UserLogoService) Save(userID uint, req SaveLogoRequest) (*model.UserLogo, error) {
+	if req.FileSize > MaxLogoFileSize {
+		return nil, ErrLogoTooLarge
+	}
+
 	count, err := s.repo.CountByUser(userID)
 	if err != nil {
 		return nil, err