feat: add monitoring dashboard page and backend entry point.

frontend/src/pages/Monitor.tsx

@@ -477,8 +477,13 @@ export default function Monitor() {
                             min={10}
                             max={300}
                             value={pollingInterval}
-                            onChange={(e) => setPollingInterval(Number(e.target.value))}
-                            hint="自动刷新号池状态的间隔时间"
+                            onChange={(e) => {
+                                const val = parseInt(e.target.value, 10)
+                                if (!isNaN(val)) {
+                                    setPollingInterval(val)
+                                }
+                            }}
+                            hint="自动刷新号池状态的间隔时间 (10-300秒)"
                         />
                         <div className="p-4 rounded-lg bg-slate-50 dark:bg-slate-800/50">
                             <div className="flex items-center justify-between">