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

frontend/components/Header.tsx

@@ -62,6 +62,8 @@ export default function Header({
   brandMark = "image_text",
   brandLogoSize = "sq",
   brandLogoFit = "contain",
+  slogan = "",
+  sloganVisible = true,
 }: {
   initialUser: User | null;
   initialUnread?: number;
@@ -74,6 +76,8 @@ export default function Header({
   brandMark?: BrandMark;
   brandLogoSize?: BrandLogoSize;
   brandLogoFit?: BrandLogoFit;
+  slogan?: string;
+  sloganVisible?: boolean;
 }) {
   const router = useRouter();
   const pathname = usePathname();
@@ -274,6 +278,7 @@ export default function Header({
               fit={brandLogoFit}
               name={siteName}
               wordmark={wordmark}
+              slogan={sloganVisible ? slogan : ""}
               logoLight={logoLight}
               logoDark={logoDark}
             />