feat(hid): 添加 Linux 键盘与 SysRq 快捷键 (#307)

控制台增加独立快捷键菜单，提供常用组合键和 Linux SysRq 指令，虚拟键盘补充 Linux 布局。
通过可靠且有序的 WebSocket 发送组合键，取消或失败时逐一释放按键，防止修饰键残留。
执行期间避免物理键盘与虚拟键盘交错输入，断连、失焦和切换布局时停止执行。
修正焦点移动后的物理按键释放，并将原虚拟键盘组合键迁移到统一菜单。

验证：独立暂存快照前端构建通过；6 项快捷键单测及 5 组浏览器测试通过，覆盖组合键序列、失败清理、取消及键盘焦点。

Refs #307

web/src/lib/keyboardShortcuts.ts

@@ -0,0 +1,108 @@
+import { CanonicalKey as Key } from '@/types/generated'
+import { updateModifierMaskForKey } from '@/lib/keyboardMappings'
+
+export interface KeyboardShortcut {
+  id: string
+  label: string
+  description: string
+  keys: Key[]
+  destructive?: boolean
+}
+
+function combination(id: string, label: string, keys: Key[]): KeyboardShortcut {
+  return { id, label, description: id, keys }
+}
+
+export const keyboardShortcuts: KeyboardShortcut[] = [
+  combination('ctrl-alt-delete', 'Ctrl+Alt+Del', [Key.ControlLeft, Key.AltLeft, Key.Delete]),
+  combination('task-manager', 'Ctrl+Shift+Esc', [Key.ControlLeft, Key.ShiftLeft, Key.Escape]),
+  combination('switch-window', 'Alt+Tab', [Key.AltLeft, Key.Tab]),
+  combination('close-window', 'Alt+F4', [Key.AltLeft, Key.F4]),
+  combination('lock-windows', 'Win+L', [Key.MetaLeft, Key.KeyL]),
+  combination('run', 'Win+R', [Key.MetaLeft, Key.KeyR]),
+  combination('tty1', 'Ctrl+Alt+F1', [Key.ControlLeft, Key.AltLeft, Key.F1]),
+  combination('tty2', 'Ctrl+Alt+F2', [Key.ControlLeft, Key.AltLeft, Key.F2]),
+  combination('restart-x', 'Ctrl+Alt+Bksp', [Key.ControlLeft, Key.AltLeft, Key.Backspace]),
+  combination('force-quit', 'Cmd+Opt+Esc', [Key.MetaLeft, Key.AltLeft, Key.Escape]),
+]
+
+function sysrq(letter: string, key: Key, destructive = false): KeyboardShortcut {
+  return {
+    id: `sysrq-${letter.toLowerCase()}`, label: letter,
+    description: `sysrq-${letter.toLowerCase()}`, destructive,
+    keys: [Key.AltLeft, Key.PrintScreen, key],
+  }
+}
+
+export const sysrqDiagnostics = [
+  sysrq('H', Key.KeyH), sysrq('F', Key.KeyF, true),
+  sysrq('M', Key.KeyM), sysrq('T', Key.KeyT),
+]
+export const sysrqRecovery = [
+  sysrq('R', Key.KeyR), sysrq('E', Key.KeyE, true), sysrq('I', Key.KeyI, true),
+  sysrq('S', Key.KeyS), sysrq('U', Key.KeyU), sysrq('B', Key.KeyB, true),
+]
+
+export type ShortcutSender = (type: 'down' | 'up', key: Key, modifiers: number) => Promise<void>
+
+function checkCancelled(signal?: AbortSignal) {
+  if (signal?.aborted) throw signal.reason ?? new DOMException('Cancelled', 'AbortError')
+}
+
+function delay(ms: number, signal?: AbortSignal): Promise<void> {
+  checkCancelled(signal)
+  return new Promise((resolve, reject) => {
+    const abort = () => {
+      clearTimeout(timer)
+      reject(signal?.reason ?? new DOMException('Cancelled', 'AbortError'))
+    }
+    const timer = setTimeout(() => {
+      signal?.removeEventListener('abort', abort)
+      resolve()
+    }, ms)
+    signal?.addEventListener('abort', abort, { once: true })
+  })
+}
+
+/** Send on one ordered transport; always attempt to release every attempted key. */
+export async function executeKeyboardShortcut(
+  shortcut: KeyboardShortcut,
+  send: ShortcutSender,
+  options: {
+    signal?: AbortSignal
+    wait?: typeof delay
+  } = {},
+) {
+  const wait = options.wait ?? delay
+  checkCancelled(options.signal)
+  const held: Key[] = []
+  let mask = 0
+  let failure: unknown
+  try {
+    for (const key of shortcut.keys) {
+      checkCancelled(options.signal)
+      // A failed send may still have reached the device, so track it first.
+      held.push(key)
+      mask = updateModifierMaskForKey(mask, key, true)
+      await send('down', key, mask)
+      await wait(40, options.signal)
+    }
+    await wait(100, options.signal)
+  } catch (error) {
+    failure = error
+  } finally {
+    // Cleanup must not inherit cancellation, and one failed release must not
+    // prevent the remaining modifiers from being released.
+    for (const key of held.reverse()) {
+      mask = updateModifierMaskForKey(mask, key, false)
+      try {
+        await send('up', key, mask)
+        await wait(20)
+      } catch (error) {
+        failure ??= error
+      }
+    }
+  }
+  if (failure) throw failure
+  checkCancelled(options.signal)
+}