feat: 可配置站点 URL 风格

- 新增 urlStyle 工具与测试：postPath/userPath/sitePagePath 统一生成链接
- 管理端新增 UrlStylePanel 设置面板，settings 服务与 handler 适配
- 全站路由链接与 JSON-LD/sitemap 切换为统一 URL 生成
- middleware 与相关组件适配

backend/handler/setting.go

@@ -75,6 +75,8 @@ type updateSettingsRequest struct {
 
 	Levels *[]model.LevelDef `json:"levels"`
 	LevelsFx *bool           `json:"levels_fx"`
+
+	UrlStyle *string `json:"url_style"`
 }
 
 func settingsPayload(saved service.PublicSiteSettings) gin.H {
@@ -132,6 +134,8 @@ func settingsPayload(saved service.PublicSiteSettings) gin.H {
 
 		"levels": saved.Levels,
 		"levels_fx": saved.LevelsFx,
+
+		"url_style": saved.UrlStyle,
 	}
 }
 
@@ -154,7 +158,8 @@ func (req *updateSettingsRequest) hasAny() bool {
 		req.PointsReplyReward != nil || req.PointsReplyDailyCap != nil ||
 		req.PointsRecommendReward != nil || req.Levels != nil || req.LevelsFx != nil ||
 		req.PostEditLockHours != nil || req.CommentEditLockHours != nil ||
-		req.NecroReplyAfterHours != nil || req.NecroReplyPenalty != nil
+		req.NecroReplyAfterHours != nil || req.NecroReplyPenalty != nil ||
+		req.UrlStyle != nil
 }
 
 // AdminGetSettings 超管读取站点设置（与公开 payload 字段一致）
@@ -537,6 +542,16 @@ func (h *Handlers) UpdateSettings(c *gin.Context) {
 			return
 		}
 	}
+	if req.UrlStyle != nil {
+		if err := h.Setting.SetUrlStyle(*req.UrlStyle); err != nil {
+			if errors.Is(err, service.ErrInvalidSiteSetting) {
+				c.JSON(http.StatusBadRequest, gin.H{"error": "链接风格无效"})
+				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 {