refactor: 拆分 middleware/router 为单一职责文件，新增站点设置管理页面

middleware:
- 拆分 auth.go → auth.go + auth_token.go + auth_parser.go + auth_admin.go
- 拆分 csrf.go → csrf.go + csrf_token.go
- 拆分 ratelimit.go → ratelimit.go + ratelimit_core.go + ratelimit_cleanup.go
- 修复 import 未使用/缺失问题

router:
- 拆分 router.go → admin.go + api.go + frontend.go + deps_core.go + deps_extra.go

feat(admin): 站点设置管理页面
- 新增 SSR 页面 /admin/site-settings（仅 Owner）
- 审核开关 Toggle 即时保存
- 通用设置展示
- 侧边栏新增站点设置入口
- 注册 UpdateBoolSetting/GetBoolSetting API 路由

internal/router/deps_core.go

@@ -0,0 +1,39 @@
+package router
+
+import (
+	"metazone.cc/metalab/internal/config"
+	"metazone.cc/metalab/internal/controller"
+	adminCtrl "metazone.cc/metalab/internal/controller/admin"
+	"metazone.cc/metalab/internal/middleware"
+	"metazone.cc/metalab/internal/repository"
+	"metazone.cc/metalab/internal/service"
+
+	"gorm.io/gorm"
+)
+
+type dependencies struct {
+	authCtrl        *controller.AuthController
+	authMdw         *middleware.AuthMiddleware
+	settingsCtrl    *controller.SettingsController
+	messageCtrl     *controller.MessageController
+	adminCtrl       *adminCtrl.AdminController
+	auditCtrl       *adminCtrl.AuditController
+	siteSettingCtrl *adminCtrl.SiteSettingController
+	tokenCtrl       *controller.AuthController
+}
+
+func buildDepsCore(db *gorm.DB, cfg *config.Config) (
+	*repository.UserRepo, *service.TokenService, *service.AuthService,
+	*middleware.RateLimiter, *controller.AuthController,
+	*service.AvatarService, *middleware.AuthMiddleware, *adminCtrl.AdminController,
+) {
+	userRepo := repository.NewUserRepo(db)
+	tokenSvc := service.NewTokenService(cfg, userRepo)
+	authService := service.NewAuthService(userRepo, tokenSvc, cfg)
+	rateLimiter := middleware.NewRateLimiter()
+	authCtrl := controller.NewAuthController(authService, tokenSvc, rateLimiter, cfg)
+	avatarSvc := service.NewAvatarService(userRepo)
+	authMdw := middleware.NewAuthMiddleware(cfg, userRepo)
+	adminController := adminCtrl.NewAdminController(service.NewAdminService(userRepo))
+	return userRepo, tokenSvc, authService, rateLimiter, authCtrl, avatarSvc, authMdw, adminController
+}