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/service/media_library_test.go

@@ -25,7 +25,7 @@ func newMediaLibraryService(t *testing.T) (*UploadService, string) {
 	if err != nil {
 		t.Fatalf("open sqlite: %v", err)
 	}
-	if err := db.AutoMigrate(&model.Attachment{}, &model.User{}, &model.Post{}, &model.Comment{}); err != nil {
+	if err := db.AutoMigrate(&model.Attachment{}, &model.Blob{}, &model.User{}, &model.Post{}, &model.Comment{}); err != nil {
 		t.Fatalf("migrate: %v", err)
 	}
 	dir := t.TempDir()
@@ -315,6 +315,82 @@ func TestAdminMediaLibraryBookCategory(t *testing.T) {
 	}
 }
 
+func TestAdminMediaLibraryDedupAggregation(t *testing.T) {
+	s, dir := newMediaLibraryService(t)
+
+	writeMediaFile(t, dir, "images/dup.webp", []byte("fake-webp-bytes"))
+
+	mkUser := func(username, nickname string) model.User {
+		if err := s.db.Create(&model.User{Username: username, Nickname: nickname}).Error; err != nil {
+			t.Fatalf("create user: %v", err)
+		}
+		var u model.User
+		if err := s.db.Where("username = ?", username).First(&u).Error; err != nil {
+			t.Fatalf("load user: %v", err)
+		}
+		return u
+	}
+	alice := mkUser("alice", "爱丽丝")
+	bob := mkUser("bob", "阿Bob")
+
+	early := time.Date(2026, 9, 1, 10, 0, 0, 0, time.UTC)
+	late := early.Add(2 * time.Hour)
+
+	// 同一张图被两人先后上传（内容寻址去重后共享同一文件/对象）
+	mkAtt := func(u model.User, url string, at time.Time) {
+		if err := s.db.Create(&model.Attachment{
+			UserID: u.ID, Kind: model.AttachmentKindImage,
+			URL: url, MIME: "image/webp",
+			Size: 100, Width: 10, Height: 10, CreatedAt: at,
+		}).Error; err != nil {
+			t.Fatalf("create attachment %s: %v", url, err)
+		}
+	}
+	mkAtt(alice, "/uploads/images/dup.webp", early)
+	mkAtt(bob, "/uploads/images/dup.webp", late)
+	mkAtt(bob, "/api/media/rdup", early)
+	mkAtt(alice, "/api/media/rdup", late)
+
+	items, _, err := s.AdminMediaLibrary()
+	if err != nil {
+		t.Fatalf("AdminMediaLibrary: %v", err)
+	}
+
+	countByURL := map[string]int{}
+	byURL := map[string]MediaLibraryItem{}
+	for _, it := range items {
+		countByURL[it.URL]++
+		byURL[it.URL] = it
+	}
+
+	// 本地去重文件：单个条目，上传者/时间取最早上传的爱丽丝，引用计数 2
+	local, ok := byURL["/uploads/images/dup.webp"]
+	if !ok {
+		t.Fatal("dedup local file missing")
+	}
+	if countByURL["/uploads/images/dup.webp"] != 1 {
+		t.Fatal("dedup local file should appear exactly once")
+	}
+	if local.Uploader != "爱丽丝" || local.RefCount != 2 {
+		t.Fatalf("local dedup meta wrong: %+v", local)
+	}
+	if local.UploadedAt == nil || !local.UploadedAt.Equal(early) {
+		t.Fatalf("local dedup time should be earliest upload, got %v", local.UploadedAt)
+	}
+
+	// 远程对象同 URL 两条记录：也只出一个条目，取最早的 bob
+	remote, ok := byURL["/api/media/rdup"]
+	if !ok {
+		t.Fatal("dedup remote object missing")
+	}
+	if countByURL["/api/media/rdup"] != 1 {
+		t.Fatal("dedup remote object should appear exactly once")
+	}
+	if remote.Uploader != "阿Bob" || remote.RefCount != 2 {
+		t.Fatalf("remote dedup meta wrong: %+v", remote)
+	}
+}
+
 func TestMediaThumb(t *testing.T) {
 	s, dir := newMediaLibraryService(t)