fix: worker 进程并发 double-close panic + 状态页连接语义重构 + 集群页骨架

- process: spawn 不再重复起 supervise goroutine（Restart 触发旧 supervise close doneCh 后再 close → panic）；新增 closeOnce/supervising 守卫；Start 首次起 supervise，重启循环在同一 goroutine 内

- httpapi: status 增加 connState（connected/connecting/failed/not_started/disabled），由 worker 日志探测真实 frps 连接（不再把本地 worker 状态误当远程 frps 状态）

- StatusView: 远程卡片主状态改为连接状态徽标；启停按钮标注为控制本地 frpc worker；本地转发区保留 worker 状态显示

- 新增 ClusterView 集群页骨架（M3 LB+健康检查载体）+ App.vue 导航接入

- render: bandwidthLimit 从 proxy 顶层移入 transport 段（frpc 0.61 正确 schema，修复真实连不上的 bug）

web/src/App.vue

@@ -13,11 +13,15 @@
         <button class="nav-btn" :class="{ active: view === 'settings' }" @click="view = 'settings'">
           设置
         </button>
+        <button class="nav-btn" :class="{ active: view === 'cluster' }" @click="view = 'cluster'">
+          集群
+        </button>
       </nav>
     </header>
     <main class="content">
       <CanvasView v-if="view === 'canvas'" />
       <SettingsView v-else-if="view === 'settings'" />
+      <ClusterView v-else-if="view === 'cluster'" />
       <StatusView v-else />
     </main>
   </div>
@@ -28,8 +32,9 @@ import { ref } from 'vue'
 import CanvasView from './views/CanvasView.vue'
 import SettingsView from './views/SettingsView.vue'
 import StatusView from './views/StatusView.vue'
+import ClusterView from './views/ClusterView.vue'
 
-const view = ref<'canvas' | 'settings' | 'status'>('status')
+const view = ref<'canvas' | 'settings' | 'status' | 'cluster'>('status')
 </script>
 
 <style>