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_extra.go

@@ -0,0 +1,38 @@
+package router
+
+import (
+	"metazone.cc/metalab/internal/config"
+	"metazone.cc/metalab/internal/controller"
+	adminCtrl "metazone.cc/metalab/internal/controller/admin"
+	"metazone.cc/metalab/internal/repository"
+	"metazone.cc/metalab/internal/service"
+
+	"gorm.io/gorm"
+)
+
+func buildDeps(db *gorm.DB, cfg *config.Config, siteSettings *config.SiteSettings) *dependencies {
+	userRepo, _, authService, _, authCtrl, avatarSvc, authMdw, adminController := buildDepsCore(db, cfg)
+
+	auditRepo := repository.NewAuditRepo(db)
+	notificationRepo := repository.NewNotificationRepo(db)
+	notificationService := service.NewNotificationService(notificationRepo)
+	auditService := service.NewAuditService(auditRepo, userRepo, siteSettings, cfg.Audit, notificationService)
+	auditController := adminCtrl.NewAuditController(auditService, userRepo)
+
+	messageController := controller.NewMessageController(notificationService)
+
+	settingsCtrl := controller.NewSettingsController(authService, avatarSvc, auditService)
+	siteSettingController := adminCtrl.NewSiteSettingController(
+		service.NewSiteSettingService(siteSettings),
+		&service.AuditDefaults{
+			Enabled: cfg.Audit.Enabled, UsernameAudit: cfg.Audit.UsernameAudit,
+			AvatarAudit: cfg.Audit.AvatarAudit, BioAudit: cfg.Audit.BioAudit,
+		},
+	)
+
+	return &dependencies{
+		authCtrl: authCtrl, authMdw: authMdw, settingsCtrl: settingsCtrl,
+		messageCtrl: messageController, adminCtrl: adminController,
+		auditCtrl: auditController, siteSettingCtrl: siteSettingController, tokenCtrl: authCtrl,
+	}
+}