Fix: 修复终端标签切换时重连问题

将终端工作区提升为主布局常驻层，离开终端路由时只隐藏不卸载组件。
新增活动终端显隐状态跟踪，页面恢复时自动重新适配尺寸和聚焦。

改动范围：
- frontend/src/layouts/MainLayout.vue
- frontend/src/views/TerminalWorkspaceView.vue
- frontend/src/components/TerminalWidget.vue

frontend/src/components/TerminalWidget.vue

@@ -1,5 +1,5 @@
 <script setup lang="ts">
-import { ref, onMounted, onUnmounted } from 'vue'
+import { nextTick, ref, onMounted, onUnmounted, watch } from 'vue'
 import { Terminal } from 'xterm'
 import { AttachAddon } from '@xterm/addon-attach'
 import { FitAddon } from '@xterm/addon-fit'
@@ -8,6 +8,7 @@ import 'xterm/css/xterm.css'
 
 const props = defineProps<{
   connectionId: number
+  active?: boolean
 }>()
 
 const containerRef = ref<HTMLElement | null>(null)
@@ -19,6 +20,21 @@ let fitAddon: FitAddon | null = null
 let ws: WebSocket | null = null
 let resizeObserver: ResizeObserver | null = null
 
+function fitTerminal() {
+  fitAddon?.fit()
+}
+
+function focusTerminal() {
+  term?.focus()
+}
+
+function refreshTerminalLayout() {
+  nextTick(() => {
+    fitTerminal()
+    focusTerminal()
+  })
+}
+
 function getWsUrl(): string {
   const authStore = useAuthStore()
   const token = authStore.token
@@ -72,7 +88,7 @@ onMounted(() => {
   fitAddon = new FitAddon()
   term.loadAddon(fitAddon)
   term.open(containerRef.value)
-  fitAddon.fit()
+  fitTerminal()
 
   try {
     ws = new WebSocket(getWsUrl())
@@ -86,7 +102,7 @@ onMounted(() => {
     status.value = 'connected'
     const attachAddon = new AttachAddon(ws!)
     term!.loadAddon(attachAddon)
-    fitAddon?.fit()
+    refreshTerminalLayout()
   }
 
   ws.onerror = () => {
@@ -103,9 +119,19 @@ onMounted(() => {
   }
 
   resizeObserver = new ResizeObserver(() => {
-    fitAddon?.fit()
+    fitTerminal()
   })
   resizeObserver.observe(containerRef.value)
+
+  if (props.active !== false) {
+    refreshTerminalLayout()
+  }
+})
+
+watch(() => props.active, (active) => {
+  if (active) {
+    refreshTerminalLayout()
+  }
 })
 
 onUnmounted(() => {

frontend/src/layouts/MainLayout.vue

@@ -4,6 +4,7 @@ import { RouterLink, useRoute, useRouter } from 'vue-router'
 import { useAuthStore } from '../stores/auth'
 import { useConnectionsStore } from '../stores/connections'
 import { useTerminalTabsStore } from '../stores/terminalTabs'
+import TerminalWorkspaceView from '../views/TerminalWorkspaceView.vue'
 import { ArrowLeftRight, Server, LogOut, Menu, X, Terminal } from 'lucide-vue-next'
 
 const route = useRoute()
@@ -14,6 +15,8 @@ const tabsStore = useTerminalTabsStore()
 const sidebarOpen = ref(false)
 
 const terminalTabs = computed(() => tabsStore.tabs)
+const showTerminalWorkspace = computed(() => route.path === '/terminal')
+const keepTerminalWorkspaceMounted = computed(() => showTerminalWorkspace.value || terminalTabs.value.length > 0)
 
 connectionsStore.fetchConnections().catch(() => {})
 
@@ -120,7 +123,12 @@ function handleTabClose(tabId: string, event: Event) {
       @click="sidebarOpen = false"
     />
     <main class="flex-1 overflow-auto min-w-0">
-      <RouterView />
+      <div v-if="keepTerminalWorkspaceMounted" v-show="showTerminalWorkspace" class="h-full">
+        <TerminalWorkspaceView :visible="showTerminalWorkspace" />
+      </div>
+      <RouterView v-slot="{ Component }">
+        <component :is="Component" v-if="!showTerminalWorkspace" />
+      </RouterView>
     </main>
   </div>
 </template>

frontend/src/views/TerminalWorkspaceView.vue

@@ -4,6 +4,10 @@ import { useTerminalTabsStore } from '../stores/terminalTabs'
 import { useConnectionsStore } from '../stores/connections'
 import TerminalWidget from '../components/TerminalWidget.vue'
 
+const props = defineProps<{
+  visible?: boolean
+}>()
+
 const tabsStore = useTerminalTabsStore()
 const connectionsStore = useConnectionsStore()
 
@@ -34,7 +38,10 @@ onMounted(() => {
           v-show="tab.active"
           class="h-full"
         >
-          <TerminalWidget :connection-id="tab.connectionId" />
+          <TerminalWidget
+            :connection-id="tab.connectionId"
+            :active="tab.active && props.visible !== false"
+          />
         </div>
       </div>
     </div>