feat(marketing): add user logo management module

Users can now save uploaded logos to the backend (marketing_user_logos table),
avoiding repeated uploads. Includes CRUD endpoints: list, save, delete with
a per-user limit of 10 logos.

Made-with: Cursor

internal/marketing/model/user_logo.go

@@ -0,0 +1,16 @@
+package model
+
+import "time"
+
+type UserLogo struct {
+	ID        uint      `json:"id" gorm:"primaryKey;comment:主键ID"`
+	UserID    uint      `json:"user_id" gorm:"not null;index;comment:用户ID"`
+	URL       string    `json:"url" gorm:"size:500;not null;comment:Logo CDN地址"`
+	Filename  string    `json:"filename" gorm:"size:255;comment:原始文件名"`
+	FileSize  int64     `json:"file_size" gorm:"comment:文件大小(字节)"`
+	CreatedAt time.Time `json:"created_at" gorm:"comment:创建时间"`
+}
+
+func (UserLogo) TableName() string {
+	return "marketing_user_logos"
+}