feat(web): add Vue workspace with file tree, tabs, autosave and live sync

- Login and first-run setup screens
- File tree with inline create/rename, context menu, drag-and-drop
  move and trash with undo; all operations update the UI first and roll
  back on failure
- Tabs keep a CodeMirror state each; edits autosave after 500 ms with
  If-Match revisions, unsent edits persist in IndexedDB, and conflicts
  or remote deletions surface as banners with explicit choices
- WebSocket events sync external edits, moves and deletions into open
  tabs; reconnects trigger a full resync
- Pasted or dropped images show instantly and upload to note.assets/
- Responsive layout with a swipe-in sidebar drawer on phones
- Switch to TypeScript 6: vue-tsc does not support TypeScript 7 yet

web/src/app/events.ts

@@ -0,0 +1,48 @@
+// 订阅服务端的仓库变更事件；断线后指数退避重连，重连成功时触发全量同步
+
+export interface VaultEvent {
+  type: 'tree' | 'changed' | 'deleted' | 'moved'
+  path?: string
+  from?: string
+  rev?: string
+}
+
+export function connectEvents(handlers: { onEvents: (evs: VaultEvent[]) => void; onResync: () => void }): () => void {
+  let ws: WebSocket | undefined
+  let delay = 1000
+  let timer: ReturnType<typeof setTimeout> | undefined
+  let stopped = false
+  let connectedBefore = false
+
+  const connect = () => {
+    const proto = location.protocol === 'https:' ? 'wss:' : 'ws:'
+    ws = new WebSocket(`${proto}//${location.host}/api/v1/events`)
+    ws.onopen = () => {
+      delay = 1000
+      // 首次连接前的状态由初始化加载，之后每次重连都可能错过事件
+      if (connectedBefore) handlers.onResync()
+      connectedBefore = true
+    }
+    ws.onmessage = (e) => handlers.onEvents(JSON.parse(e.data))
+    ws.onclose = () => {
+      if (stopped) return
+      timer = setTimeout(connect, delay)
+      delay = Math.min(delay * 2, 30000)
+    }
+  }
+  connect()
+  // 页面从后台恢复时立即重连，不等退避计时
+  const onVisible = () => {
+    if (document.visibilityState === 'visible' && ws?.readyState === WebSocket.CLOSED) {
+      clearTimeout(timer)
+      connect()
+    }
+  }
+  document.addEventListener('visibilitychange', onVisible)
+  return () => {
+    stopped = true
+    clearTimeout(timer)
+    document.removeEventListener('visibilitychange', onVisible)
+    ws?.close()
+  }
+}