feat: 支持应用内多 SSH 终端标签页

- 新增 terminalTabs store 管理标签页状态
- 新增 TerminalWorkspaceView 终端工作区视图
- 修改 ConnectionsView 终端按钮改用标签页模式
- 修改 TerminalView 作为兼容入口自动跳转到工作区
- 同一连接默认只保留一个标签页
- 切换标签时保持各自 SSH 会话不断开

frontend/src/stores/terminalTabs.ts

@@ -0,0 +1,74 @@
+import { defineStore } from 'pinia'
+import { ref, computed } from 'vue'
+import type { Connection } from '../api/connections'
+
+export interface TerminalTab {
+  id: string
+  connectionId: number
+  title: string
+  active: boolean
+}
+
+export const useTerminalTabsStore = defineStore('terminalTabs', () => {
+  const tabs = ref<TerminalTab[]>([])
+  const activeTabId = ref<string | null>(null)
+
+  const activeTab = computed(() => tabs.value.find(t => t.id === activeTabId.value) || null)
+
+  function generateTabId() {
+    return `tab-${Date.now()}-${Math.random().toString(16).slice(2)}`
+  }
+
+  function openOrFocus(connection: Connection) {
+    // 检查是否已存在该连接的标签页
+    const existing = tabs.value.find(t => t.connectionId === connection.id)
+    if (existing) {
+      activate(existing.id)
+      return existing.id
+    }
+
+    // 创建新标签页
+    const newTab: TerminalTab = {
+      id: generateTabId(),
+      connectionId: connection.id,
+      title: connection.name,
+      active: true,
+    }
+
+    tabs.value.push(newTab)
+    activate(newTab.id)
+    return newTab.id
+  }
+
+  function activate(tabId: string) {
+    tabs.value.forEach(t => {
+      t.active = t.id === tabId
+    })
+    activeTabId.value = tabId
+  }
+
+  function close(tabId: string) {
+    const index = tabs.value.findIndex(t => t.id === tabId)
+    if (index === -1) return
+
+    const wasActive = tabs.value[index]!.active
+    tabs.value.splice(index, 1)
+
+    // 如果关闭的是活动标签，激活相邻标签
+    if (wasActive && tabs.value.length > 0) {
+      const newIndex = Math.min(index, tabs.value.length - 1)
+      activate(tabs.value[newIndex]!.id)
+    } else if (tabs.value.length === 0) {
+      activeTabId.value = null
+    }
+  }
+
+  return {
+    tabs,
+    activeTabId,
+    activeTab,
+    openOrFocus,
+    activate,
+    close,
+  }
+})