feat: 友链/书库/移动端导航/排行榜等多模块功能

新增模块：
- 友链（friendlink）后端处理 + 前端管理页与友链板
- 书库（library）：导入、章节、封面、阅读页、横竖版自适应 AdaptiveCoverSlot
- 顶栏导航（header_nav）配置与 MobileTabBar/MobileRailDrawers 移动端抽屉
- 排行榜 service 测试、站点页面测试、时间线发布（timeline_release）

其它改动：
- 后端 handlers/services 全量小幅调整
- 前端组件、库函数、URL/品牌/站点 URL 工具更新
- Lightbox 图片、MdEntries 条目卡、coverColor 派生色相等前端能力

backend/handler/setting.go

@@ -73,10 +73,14 @@ type updateSettingsRequest struct {
 	NecroReplyAfterHours *int `json:"necro_reply_after_hours"`
 	NecroReplyPenalty    *int `json:"necro_reply_penalty"`
 
-	Levels *[]model.LevelDef `json:"levels"`
-	LevelsFx *bool           `json:"levels_fx"`
+	Levels   *[]model.LevelDef `json:"levels"`
+	LevelsFx *bool             `json:"levels_fx"`
 
 	UrlStyle *string `json:"url_style"`
+
+	MobileTabs *[]string `json:"mobile_tabs"`
+
+	HeaderNav *[]service.HeaderNavItem `json:"header_nav"`
 }
 
 func settingsPayload(saved service.PublicSiteSettings) gin.H {
@@ -87,9 +91,9 @@ func settingsPayload(saved service.PublicSiteSettings) gin.H {
 		"site_name":              saved.SiteName,
 		"site_description":       saved.SiteDescription,
 		"allow_register":         saved.AllowRegister,
-		"allow_comments":          saved.AllowComments,
-		"comments_require_login":  saved.CommentsRequireLogin,
-		"allow_messages":          saved.AllowMessages,
+		"allow_comments":         saved.AllowComments,
+		"comments_require_login": saved.CommentsRequireLogin,
+		"allow_messages":         saved.AllowMessages,
 		"post_cooldown_hours":    saved.PostCooldownHours,
 		"code_block_auto_fold":   saved.CodeBlockAutoFold,
 		"code_block_fold_lines":  saved.CodeBlockFoldLines,
@@ -127,15 +131,19 @@ func settingsPayload(saved service.PublicSiteSettings) gin.H {
 		"points_reply_daily_cap":   saved.PointsReplyDailyCap,
 		"points_recommend_reward":  saved.PointsRecommendReward,
 
-		"post_edit_lock_hours":     saved.PostEditLockHours,
-		"comment_edit_lock_hours":  saved.CommentEditLockHours,
-		"necro_reply_after_hours":  saved.NecroReplyAfterHours,
-		"necro_reply_penalty":      saved.NecroReplyPenalty,
+		"post_edit_lock_hours":    saved.PostEditLockHours,
+		"comment_edit_lock_hours": saved.CommentEditLockHours,
+		"necro_reply_after_hours": saved.NecroReplyAfterHours,
+		"necro_reply_penalty":     saved.NecroReplyPenalty,
 
-		"levels": saved.Levels,
+		"levels":    saved.Levels,
 		"levels_fx": saved.LevelsFx,
 
 		"url_style": saved.UrlStyle,
+
+		"mobile_tabs": saved.MobileTabs,
+
+		"header_nav": saved.HeaderNav,
 	}
 }
 
@@ -159,7 +167,7 @@ func (req *updateSettingsRequest) hasAny() bool {
 		req.PointsRecommendReward != nil || req.Levels != nil || req.LevelsFx != nil ||
 		req.PostEditLockHours != nil || req.CommentEditLockHours != nil ||
 		req.NecroReplyAfterHours != nil || req.NecroReplyPenalty != nil ||
-		req.UrlStyle != nil
+		req.UrlStyle != nil || req.MobileTabs != nil || req.HeaderNav != nil
 }
 
 // AdminGetSettings 超管读取站点设置（与公开 payload 字段一致）
@@ -552,6 +560,26 @@ func (h *Handlers) UpdateSettings(c *gin.Context) {
 			return
 		}
 	}
+	if req.MobileTabs != nil {
+		if err := h.Setting.SetMobileTabs(*req.MobileTabs); err != nil {
+			if errors.Is(err, service.ErrInvalidSiteSetting) {
+				c.JSON(http.StatusBadRequest, gin.H{"error": "移动端底栏配置无效（至少保留一项，且取值须在允许列表内）"})
+				return
+			}
+			c.JSON(http.StatusInternalServerError, gin.H{"error": "保存站点设置失败"})
+			return
+		}
+	}
+	if req.HeaderNav != nil {
+		if err := h.Setting.SetHeaderNav(*req.HeaderNav); err != nil {
+			if errors.Is(err, service.ErrInvalidSiteSetting) {
+				c.JSON(http.StatusBadRequest, gin.H{"error": "顶部导航配置无效（最多 8 项，内置项须在允许列表内，自定义项名称 1–16 字、地址须为站内路径或 http(s)）"})
+				return
+			}
+			c.JSON(http.StatusInternalServerError, gin.H{"error": "保存站点设置失败"})
+			return
+		}
+	}
 
 	saved, err := h.Setting.Public()
 	if err != nil {