feat: 公告系统 — Phase 2 完成

- Model/Repo/Service/Controller 全栈实现
- CRUD + ListActive（生效时间范围过滤）
- 管理后台独立页面 /admin/announcements（列表+弹窗CRUD）
- 前台首页 Hero 下方公告栏（info/success/warning/error 四色）
- Moderator+ 权限可管理公告

internal/router/deps_extra.go

@@ -103,6 +103,11 @@ func buildDeps(db *gorm.DB, cfg *config.Config, siteSettings *config.SiteSetting
 
 	maintenanceMdw := middleware.NewMaintenanceMiddleware(cfg, siteSettings, sessionMgr)
 
+	// 公告系统
+	announcementRepo := repository.NewAnnouncementRepo(db)
+	announcementService := service.NewAnnouncementService(announcementRepo)
+	announcementCtrl := adminCtrl.NewAnnouncementController(announcementService)
+
 	// 首页内存缓存（30s TTL），文章变更时失效
 	homeCache := cache.NewHomePageCache(30 * time.Second)
 	postService.WithHomePageInvalidator(func() { homeCache.Invalidate() })
@@ -126,7 +131,9 @@ func buildDeps(db *gorm.DB, cfg *config.Config, siteSettings *config.SiteSetting
 		followCtrl:      followCtrl,
 		favoriteCtrl:    favoriteCtrl,
 		favoriteService: favoriteService,
-		trendsService:   trendsService,
-		homeCache:       homeCache,
+		trendsService:      trendsService,
+		homeCache:          homeCache,
+		announcementService: announcementService,
+		announcementCtrl:   announcementCtrl,
 	}
 }