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/Icon.vue

@@ -0,0 +1,34 @@
+<script setup lang="ts">
+// 线性图标（24×24 视框，描边绘制）
+const paths = {
+  menu: 'M4 6h16M4 12h16M4 18h16',
+  noteAdd: 'M14 3H6a2 2 0 0 0-2 2v14a2 2 0 0 0 2 2h12a2 2 0 0 0 2-2V9zM14 3v6h6M12 12v6M9 15h6',
+  folderAdd: 'M3 7a2 2 0 0 1 2-2h4l2 2h8a2 2 0 0 1 2 2v8a2 2 0 0 1-2 2H5a2 2 0 0 1-2-2zM12 10v6M9 13h6',
+  folder: 'M3 7a2 2 0 0 1 2-2h4l2 2h8a2 2 0 0 1 2 2v8a2 2 0 0 1-2 2H5a2 2 0 0 1-2-2z',
+  note: 'M14 3H6a2 2 0 0 0-2 2v14a2 2 0 0 0 2 2h12a2 2 0 0 0 2-2V9zM14 3v6h6',
+  chevron: 'm9 6 6 6-6 6',
+  more: 'M12 6h.01M12 12h.01M12 18h.01',
+  close: 'M18 6 6 18M6 6l12 12',
+  trash: 'M3 6h18M8 6V4a1 1 0 0 1 1-1h6a1 1 0 0 1 1 1v2M19 6l-1 14a2 2 0 0 1-2 2H8a2 2 0 0 1-2-2L5 6',
+  logout: 'M9 21H5a2 2 0 0 1-2-2V5a2 2 0 0 1 2-2h4M16 17l5-5-5-5M21 12H9',
+  restore: 'M3 12a9 9 0 1 0 3-6.7L3 8M3 3v5h5',
+  edit: 'M12 20h9M16.5 3.5a2.1 2.1 0 0 1 3 3L7 19l-4 1 1-4z',
+}
+defineProps<{ name: keyof typeof paths; size?: number }>()
+</script>
+
+<template>
+  <svg
+    :width="size ?? 16"
+    :height="size ?? 16"
+    viewBox="0 0 24 24"
+    fill="none"
+    stroke="currentColor"
+    stroke-width="2"
+    stroke-linecap="round"
+    stroke-linejoin="round"
+    aria-hidden="true"
+  >
+    <path :d="paths[name]" />
+  </svg>
+</template>