接入运维真实 metrics：负载、请求错误率与服务探测

- 新增 GET /admin/ops/metrics 与进程内请求统计中间件
- 运维页展示 CPU/内存/磁盘、24h 曲线与 WS/DB/存储状态
- 去掉未使用的消息队列占位项

server/internal/handler/admin.go

@@ -10,11 +10,16 @@ import (
 	"golang.org/x/crypto/bcrypt"
 	"kefu-sys/server/internal/middleware"
 	"kefu-sys/server/internal/model"
+	"kefu-sys/server/internal/storage"
 )
 
-type AdminHandler struct{}
+type AdminHandler struct {
+	store storage.ObjectStorage
+}
 
-func NewAdminHandler() *AdminHandler { return &AdminHandler{} }
+func NewAdminHandler(store storage.ObjectStorage) *AdminHandler {
+	return &AdminHandler{store: store}
+}
 
 func (h *AdminHandler) Stats(c *gin.Context) {
 	var tenantTotal, activeTotal, suspendedTotal, expiringTotal, newThisMonth int64