feat: 媒体库 blob 去重存储与品牌/注册等前端调整

新增：
- blob_store 二进制去重存储 + blob_dedup 测试

其它：
- 后端 settings/auth/media_library/upload/operations 服务与 handler 调整
- 前端品牌（BrandLockup/BrandCropModal/BrandSeoPanel）、注册、媒体库、分析详情页、Header/SiteChrome 等更新

backend/model/operations.go

@@ -51,7 +51,7 @@ type EmailChallenge struct {
 
 // Every remote object pins the immutable configuration revision that wrote it.
 type StoredObject struct {
-	ID         string    `gorm:"primaryKey;size:64" json:"id"`
+	ID         string    `gorm:"primaryKey;size:96" json:"id"`
 	ConfigName string    `gorm:"size:64;index" json:"-"`
 	Key        string    `gorm:"size:512" json:"-"`
 	MIME       string    `gorm:"size:128" json:"-"`