Add command palette and command registry

- Commands (with optional shortcuts and availability checks) are registered in one place;
  global shortcuts are dispatched from it, and plugins can use registerCommand later
- The quick switcher lists commands when the input starts with '>' (VS Code style),
  opened with Ctrl+Shift+P or F1 (Firefox reserves Ctrl+Shift+P), plus buttons in the
  sidebar footer and the mobile top bar; recently used commands come first
- Built-in commands: quick open, search, new note/folder, save, rename, delete, close tab,
  trash, log out
- Mount the trash dialog at the workspace level so it is not positioned inside the
  transformed mobile drawer

web/src/app/commands.ts

@@ -0,0 +1,62 @@
+// 命令注册表：命令面板列出的操作与全局快捷键都来自这里；插件也通过 registerCommand 添加命令
+import { shallowReactive } from 'vue'
+
+export interface Command {
+  id: string
+  title: string
+  /** 快捷键，如 'Mod+Shift+F'、'F1'；Mod 在 Mac 上为 Cmd，其他平台为 Ctrl。第一个用于显示 */
+  keys?: string[]
+  /** 返回 false 时命令不可用：不在面板中列出，快捷键也不触发 */
+  when?: () => boolean
+  run: () => void
+}
+
+const commands = shallowReactive(new Map<string, Command>())
+
+/** 注册命令，返回注销函数；id 重复时后注册的覆盖先注册的 */
+export function registerCommand(cmd: Command): () => void {
+  commands.set(cmd.id, cmd)
+  return () => {
+    if (commands.get(cmd.id) === cmd) commands.delete(cmd.id)
+  }
+}
+
+export function availableCommands(): Command[] {
+  return [...commands.values()].filter((c) => c.when?.() ?? true)
+}
+
+export function runCommand(id: string) {
+  const cmd = commands.get(id)
+  if (cmd && (cmd.when?.() ?? true)) cmd.run()
+}
+
+const isMac = /Mac|iPhone|iPad/.test(navigator.platform)
+
+export function matchKeys(e: KeyboardEvent, keys: string): boolean {
+  const parts = keys.split('+')
+  const key = parts.pop()!.toLowerCase()
+  return (
+    e.key.toLowerCase() === key &&
+    (isMac ? e.metaKey : e.ctrlKey) === parts.includes('Mod') &&
+    e.shiftKey === parts.includes('Shift') &&
+    e.altKey === parts.includes('Alt')
+  )
+}
+
+export function formatKeys(keys: string): string {
+  const parts = keys.split('+')
+  if (isMac) return parts.map((p) => ({ Mod: '⌘', Shift: '⇧', Alt: '⌥' })[p] ?? p).join('')
+  return parts.map((p) => (p === 'Mod' ? 'Ctrl' : p)).join('+')
+}
+
+/** 全局快捷键分发；编辑器等已处理的按键（defaultPrevented）和输入法组字中的按键不处理 */
+export function handleShortcut(e: KeyboardEvent) {
+  if (e.defaultPrevented || e.isComposing) return
+  for (const cmd of availableCommands()) {
+    if (cmd.keys?.some((k) => matchKeys(e, k))) {
+      e.preventDefault()
+      cmd.run()
+      return
+    }
+  }
+}