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/admin.go

@@ -0,0 +1,57 @@
+package router
+
+import (
+	"metazone.cc/metalab/internal/config"
+	"metazone.cc/metalab/internal/middleware"
+	"metazone.cc/metalab/internal/model"
+
+	"github.com/gin-gonic/gin"
+)
+
+// setupAdminRoutes 注册管理后台页面和 API 路由
+func setupAdminRoutes(r *gin.Engine, cfg *config.Config, d *dependencies) {
+	// --- 管理后台 SSR 页面 ---
+	adminPages := r.Group("/admin")
+	adminPages.Use(d.authMdw.AdminAuth())
+	adminPages.Use(middleware.RequirePageRole(model.RoleModerator))
+	adminPages.Use(middleware.CSRF(cfg))
+	adminPages.Use(func(c *gin.Context) {
+		middleware.SetCSRFToken(c, cfg)
+		c.Next()
+	})
+	{
+		adminPages.GET("/", d.adminCtrl.Dashboard)
+		adminPages.GET("/users", d.adminCtrl.UsersPage,
+			middleware.RequirePageRole(model.RoleAdmin))
+		adminPages.GET("/audits", d.auditCtrl.AuditPage,
+			middleware.RequirePageRole(model.RoleAdmin))
+		adminPages.GET("/site-settings", d.siteSettingCtrl.SiteSettingsPage,
+			middleware.RequirePageRole(model.RoleOwner))
+	}
+
+	// --- 管理后台 API ---
+	adminAPI := r.Group("/api/admin")
+	adminAPI.Use(d.authMdw.Required())
+	adminAPI.Use(middleware.RequireMinRole(model.RoleAdmin))
+	adminAPI.Use(middleware.CSRF(cfg))
+	{
+		adminAPI.GET("/users", d.adminCtrl.ListUsers)
+		adminAPI.PUT("/users/:uid/status", d.adminCtrl.UpdateUserStatus)
+		adminAPI.POST("/users/:uid/reset-token", d.adminCtrl.ResetToken)
+		adminAPI.GET("/audits", d.auditCtrl.ListAudits)
+		adminAPI.POST("/audits/:id/approve", d.auditCtrl.Approve)
+		adminAPI.POST("/audits/:id/reject", d.auditCtrl.Reject)
+	}
+
+	// --- 站点设置 API（仅 owner） ---
+	siteSettingsAPI := r.Group("/api/admin/site-settings")
+	siteSettingsAPI.Use(d.authMdw.Required())
+	siteSettingsAPI.Use(middleware.RequireMinRole(model.RoleOwner))
+	siteSettingsAPI.Use(middleware.CSRF(cfg))
+	{
+		siteSettingsAPI.GET("", d.siteSettingCtrl.GetSettings)
+		siteSettingsAPI.PUT("", d.siteSettingCtrl.UpdateSetting)
+		siteSettingsAPI.PUT("/bool", d.siteSettingCtrl.UpdateBoolSetting)
+		siteSettingsAPI.GET("/bool", d.siteSettingCtrl.GetBoolSetting)
+	}
+}