feat: 管理首页帖子总数统计（总数/已发布/待审核）

- PostRepo 新增 CountPostsByStatus 和 CountPending 方法
- Service 层定义 postAdminStatStore 接口 (ISP)
- AdminService 注入 postRepo，新增 PostStats 结构体和 GetPostStats 方法
- AdminController.Dashboard 调用 GetPostStats 并传参到模板
- Dashboard 帖子卡片显示总数 + 已发布 + 待审核（橙色徽章）
- DI 层将 AdminController 创建从 buildDepsCore 移至 buildDeps，以便注入 postRepo

internal/router/deps_extra.go

@@ -13,7 +13,7 @@ import (
 )
 
 func buildDeps(db *gorm.DB, cfg *config.Config, siteSettings *config.SiteSettings, redisClient *redis.Client) *dependencies {
-	userRepo, sessionMgr, authService, _, authCtrl, avatarSvc, authMdw, adminController := buildDepsCore(db, cfg, siteSettings, redisClient)
+	userRepo, sessionMgr, authService, _, authCtrl, avatarSvc, authMdw := buildDepsCore(db, cfg, siteSettings, redisClient)
 
 	auditRepo := repository.NewAuditRepo(db)
 	notificationRepo := repository.NewNotificationRepo(db)
@@ -37,6 +37,7 @@ func buildDeps(db *gorm.DB, cfg *config.Config, siteSettings *config.SiteSetting
 	shortcodeSvc := service.NewShortcodeService()
 	postCtrl := controller.NewPostController(postService, shortcodeSvc)
 	adminPostCtrl := adminCtrl.NewAdminPostController(postService)
+	adminController := adminCtrl.NewAdminController(service.NewAdminService(userRepo, postRepo, sessionMgr))
 	studioCtrl := controller.NewStudioController(postService)
 
 	// 用户空间