feat: keybar function captions + Ctrl+R/L/D, plus ⌨ shortcut cheat-sheet

keybar:
- add Ctrl+R (搜历史/\x12), Ctrl+L (重绘/\x0c), Ctrl+D (退出/\x04)
- each key now shows a short function caption under the glyph (self-documenting
  on touch where tooltips don't appear); 17 keys total
- test/keybar.test.ts updated to 17 keys

cheat-sheet (new public/shortcuts.ts):
- ⌨ toolbar button opens a grouped reference of common Claude Code shortcuts
  (general / editing / multiline / macOS / prefixes), each labeled with what it
  does; keys also on the bottom bar are tagged 键栏
- Esc / click-outside to close; styled card with sticky header + accent tags

216 tests green; tsc + build clean.

public/shortcuts.ts

@@ -0,0 +1,142 @@
+/**
+ * public/shortcuts.ts — Claude Code keyboard cheat-sheet (⌨ toolbar button).
+ *
+ * Opens an overlay listing the common Claude Code shortcuts grouped by purpose,
+ * each labeled with what it does. Keys also present on the bottom touch key bar
+ * are tagged "键栏". Source: official Claude Code interactive-mode docs.
+ */
+
+interface Shortcut {
+  keys: string
+  desc: string
+  onBar?: boolean // also available on the bottom key bar
+}
+
+interface ShortcutGroup {
+  title: string
+  items: Shortcut[]
+}
+
+const GROUPS: ShortcutGroup[] = [
+  {
+    title: '常用 General',
+    items: [
+      { keys: 'Esc', desc: '打断 Claude / 关闭弹窗', onBar: true },
+      { keys: 'Esc Esc', desc: '有输入→清空存草稿;空→打开回溯菜单', onBar: true },
+      { keys: 'Ctrl+C', desc: '中断运行;无运行时清空,再按退出', onBar: true },
+      { keys: 'Ctrl+D', desc: '退出会话 (EOF)', onBar: true },
+      { keys: 'Shift+Tab', desc: '循环权限模式 (default/acceptEdits/plan…)', onBar: true },
+      { keys: 'Ctrl+R', desc: '反向搜索命令历史', onBar: true },
+      { keys: 'Ctrl+O', desc: '切换 transcript(详细工具调用)视图', onBar: true },
+      { keys: 'Ctrl+L', desc: '重绘屏幕(显示错乱时救场)', onBar: true },
+      { keys: 'Ctrl+T', desc: '切换任务列表', onBar: true },
+      { keys: 'Ctrl+B', desc: '把命令/agent 转到后台(tmux 按两次)', onBar: true },
+      { keys: '↑ / ↓', desc: '移动光标 / 翻命令历史', onBar: true },
+      { keys: 'Tab', desc: '补全建议 / 接受提示', onBar: true },
+      { keys: '/', desc: '命令与 skill 启动器', onBar: true },
+    ],
+  },
+  {
+    title: '行内编辑 Editing',
+    items: [
+      { keys: 'Ctrl+A', desc: '光标到行首' },
+      { keys: 'Ctrl+E', desc: '光标到行尾' },
+      { keys: 'Ctrl+K', desc: '删除到行尾' },
+      { keys: 'Ctrl+U', desc: '删除到行首' },
+      { keys: 'Ctrl+W', desc: '删除前一个词' },
+      { keys: 'Ctrl+Y', desc: '粘回被删除的内容' },
+      { keys: 'Alt+B / Alt+F', desc: '按词左移 / 右移' },
+    ],
+  },
+  {
+    title: '多行输入 Multiline',
+    items: [
+      { keys: '\\ + Enter', desc: '换行(任何终端都行)' },
+      { keys: 'Shift+Enter', desc: '换行(iTerm2/WezTerm/Kitty… 原生)' },
+      { keys: 'Ctrl+J', desc: '换行(无需配置,任何终端)' },
+    ],
+  },
+  {
+    title: 'macOS(需 Option 当 Meta)',
+    items: [
+      { keys: 'Option+P', desc: '切换模型' },
+      { keys: 'Option+T', desc: '开关 extended thinking' },
+      { keys: 'Option+O', desc: '开关 fast mode' },
+    ],
+  },
+  {
+    title: '前缀 Prefixes',
+    items: [
+      { keys: '! 开头', desc: 'shell 模式,直接跑命令并入上下文' },
+      { keys: '@', desc: '文件路径补全' },
+    ],
+  },
+]
+
+export function mountShortcuts(toolbar: HTMLElement): void {
+  const overlay = document.createElement('div')
+  overlay.id = 'shortcutsmodal'
+  overlay.style.display = 'none'
+  const card = document.createElement('div')
+  card.className = 'sc-card'
+  overlay.appendChild(card)
+  document.body.appendChild(overlay)
+
+  const hide = (): void => {
+    overlay.style.display = 'none'
+  }
+  overlay.addEventListener('click', (e) => {
+    if (e.target === overlay) hide()
+  })
+  document.addEventListener('keydown', (e) => {
+    if (e.key === 'Escape' && overlay.style.display !== 'none') hide()
+  })
+
+  const build = (): void => {
+    card.replaceChildren()
+    const title = document.createElement('div')
+    title.className = 'sc-title'
+    title.textContent = 'Claude Code 快捷键'
+    card.appendChild(title)
+
+    for (const group of GROUPS) {
+      const gh = document.createElement('div')
+      gh.className = 'sc-group'
+      gh.textContent = group.title
+      card.appendChild(gh)
+
+      for (const sc of group.items) {
+        const row = document.createElement('div')
+        row.className = 'sc-row'
+
+        const key = document.createElement('span')
+        key.className = 'sc-key'
+        key.textContent = sc.keys
+
+        const desc = document.createElement('span')
+        desc.className = 'sc-desc'
+        desc.textContent = sc.desc
+
+        row.append(key, desc)
+        if (sc.onBar) {
+          const tag = document.createElement('span')
+          tag.className = 'sc-tag'
+          tag.textContent = '键栏'
+          row.appendChild(tag)
+        }
+        card.appendChild(row)
+      }
+    }
+  }
+  build()
+
+  const toggle = document.createElement('button')
+  toggle.className = 'toolbtn'
+  toggle.textContent = '⌨'
+  toggle.title = 'Claude Code 快捷键速查'
+  toggle.setAttribute('aria-label', 'Keyboard shortcuts')
+  toggle.addEventListener('click', () => {
+    overlay.style.display = overlay.style.display === 'none' ? 'flex' : 'none'
+  })
+  toolbar.appendChild(toggle)
+}