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/handler/operations.go

@@ -262,6 +262,10 @@ func (h *Handlers) SendEmailCode(c *gin.Context) {
 		return
 	}
 	wait, e := h.Ops.SendCode(req.Email, req.Purpose, c.ClientIP())
+	if errors.Is(e, service.ErrEmailRegistered) {
+		c.JSON(http.StatusBadRequest, gin.H{"error": e.Error()})
+		return
+	}
 	if !h.quotaResponse(c, wait, e) {
 		return
 	}

backend/handler/setting.go

@@ -57,6 +57,7 @@ type updateSettingsRequest struct {
 	BrandMark            *string               `json:"brand_mark"`
 	BrandLogoSize        *string               `json:"brand_logo_size"`
 	BrandLogoFit         *string               `json:"brand_logo_fit"`
+	BrandSloganVisible   *bool                 `json:"brand_slogan_visible"`
 	FooterLinks          *[]service.FooterLink `json:"footer_links"`
 
 	PointsCheckinBase     *int `json:"points_checkin_base"`
@@ -120,6 +121,7 @@ func settingsPayload(saved service.PublicSiteSettings) gin.H {
 		"brand_mark":             saved.BrandMark,
 		"brand_logo_size":        saved.BrandLogoSize,
 		"brand_logo_fit":         saved.BrandLogoFit,
+		"brand_slogan_visible":   saved.BrandSloganVisible,
 		"footer_links":           saved.FooterLinks,
 
 		"points_checkin_base":      saved.PointsCheckinBase,
@@ -160,6 +162,7 @@ func (req *updateSettingsRequest) hasAny() bool {
 		req.SiteWordmark != nil || req.SiteSlogan != nil || req.SiteKeywords != nil ||
 		req.LogoLightURL != nil || req.LogoDarkURL != nil || req.FaviconURL != nil ||
 		req.BrandMark != nil || req.BrandLogoSize != nil || req.BrandLogoFit != nil ||
+		req.BrandSloganVisible != nil ||
 		req.FooterLinks != nil ||
 		req.PointsCheckinBase != nil || req.PointsStreakEveryDays != nil || req.PointsStreakBonus != nil ||
 		req.PointsPostReward != nil || req.PointsPostDailyCap != nil ||
@@ -540,6 +543,12 @@ func (h *Handlers) UpdateSettings(c *gin.Context) {
 			return
 		}
 	}
+	if req.BrandSloganVisible != nil {
+		if err := h.Setting.SetBrandSloganVisible(*req.BrandSloganVisible); err != nil {
+			c.JSON(http.StatusInternalServerError, gin.H{"error": "保存站点设置失败"})
+			return
+		}
+	}
 	if req.FooterLinks != nil {
 		if err := h.Setting.SetFooterLinks(*req.FooterLinks); err != nil {
 			if errors.Is(err, service.ErrInvalidSiteSetting) {