feat(menus): 右键菜单与切换五项（docs/21）

屏蔽 WebView 自带右键菜单（输入框除外）；新增 useDismiss 统一修复菜单
点别处不消失（标签菜单实测中招、文件树菜单一并加固）；侧栏页签行加收起
按钮、收起后编辑区左上角有展开按钮；编辑区右下角加源码/即时渲染切换按钮；
标签与文件树右键补保存/另存为/新窗口打开/导出/打印（针对目标文件，
未打开先打开再执行）。vitest 97 通过 + 2 跳过。

tests/context-menus.test.tsx

@@ -0,0 +1,113 @@
+// 右键菜单回归（docs/21）：标签菜单与文件树菜单的文件类动作、点别处关闭。
+import { describe, it, expect, vi } from 'vitest'
+import { createRoot } from 'react-dom/client'
+import { act } from 'react-dom/test-utils'
+
+vi.mock('../src/services/platform', async (importOriginal) => {
+  const orig = await importOriginal<typeof import('../src/services/platform')>()
+  return {
+    ...orig,
+    listDir: async (dir: string) =>
+      dir === 'C:/ws' ? [{ name: 'a.md', path: 'C:/ws/a.md', isDir: false }] : [],
+  }
+})
+
+import TabBar from '../src/components/TabBar'
+import Sidebar from '../src/components/Sidebar'
+import { createTab } from '../src/stores/tabs'
+
+const sleep = (ms: number) => new Promise((r) => setTimeout(r, ms))
+
+function rightClick(el: Element) {
+  el.dispatchEvent(new MouseEvent('contextmenu', { bubbles: true, clientX: 10, clientY: 10 }))
+}
+function mouseDownOutside() {
+  document.body.dispatchEvent(new MouseEvent('mousedown', { bubbles: true }))
+}
+function menuTexts(container: HTMLElement, selector: string) {
+  const menu = container.querySelector(selector)
+  return menu ? [...menu.querySelectorAll('button')].map((b) => b.textContent) : null
+}
+
+describe('标签右键菜单', () => {
+  it('含文件类动作；动作回调带标签 id；点别处关闭', async () => {
+    const container = document.createElement('div')
+    document.body.appendChild(container)
+    const root = createRoot(container)
+    const tab = createTab({ title: 'a', content: 'x', path: 'C:/a.md' })
+    const onSaveAsTab = vi.fn()
+    await act(async () => {
+      root.render(
+        <TabBar
+          tabs={[tab]} activeId={tab.id}
+          onActivate={() => undefined} onClose={() => undefined}
+          onCloseOthers={() => undefined} onCloseRight={() => undefined}
+          onNew={() => undefined} onMove={() => undefined}
+          onSaveAsTab={onSaveAsTab}
+          onOpenInNewWindowTab={() => undefined}
+        />,
+      )
+    })
+    const tabEl = container.querySelector('.tab') as Element
+    await act(async () => { rightClick(tabEl) })
+    const texts = menuTexts(container, '.context-menu') ?? []
+    for (const label of ['另存为…', '在新窗口打开', '导出…', '打印 / 导出 PDF…', '关闭']) {
+      expect(texts.some((t) => t === label)).toBe(true)
+    }
+    // 点菜单外（文档任意处按下）→ 关闭
+    await act(async () => { mouseDownOutside() })
+    expect(container.querySelector('.context-menu')).toBeNull()
+    // 重新打开并点「另存为…」→ 回调触发且菜单关闭
+    await act(async () => { rightClick(tabEl) })
+    const saveAsBtn = [...container.querySelectorAll('.context-menu button')].find((b) => b.textContent === '另存为…')
+    await act(async () => { saveAsBtn?.dispatchEvent(new MouseEvent('click', { bubbles: true })) })
+    expect(onSaveAsTab).toHaveBeenCalledWith(tab.id)
+    expect(container.querySelector('.context-menu')).toBeNull()
+    await act(async () => { root.unmount() })
+    container.remove()
+  })
+})
+
+describe('文件树右键菜单', () => {
+  it('文件条目含打开/新窗口/另存为/导出/打印；点别处关闭', async () => {
+    const container = document.createElement('div')
+    document.body.appendChild(container)
+    const root = createRoot(container)
+    const onExportEntry = vi.fn()
+    await act(async () => {
+      root.render(
+        <Sidebar
+          mode="files" onModeChange={() => undefined}
+          workspaceRoot="C:/ws" activePath={null}
+          onOpenFile={() => undefined} onOpenFolder={() => undefined}
+          outline={[]} onJumpHeading={() => undefined} tauriMode
+          onRenameEntry={() => undefined}
+          onOpenInNewWindowEntry={() => undefined}
+          onSaveAsEntry={() => undefined}
+          onExportEntry={onExportEntry}
+          onPrintEntry={() => undefined}
+        />,
+      )
+    })
+    await act(async () => { await sleep(30) })
+    const item = [...container.querySelectorAll('.tree-item')].find((el) => el.textContent?.includes('a.md')) as Element
+    expect(item).toBeTruthy()
+    await act(async () => { rightClick(item) })
+    const texts = menuTexts(container, '.tree-context-menu') ?? []
+    for (const label of ['打开', '在新窗口打开', '另存为…', '导出…', '打印 / 导出 PDF…', '重命名…']) {
+      expect(texts.some((t) => t === label)).toBe(true)
+    }
+    const exportBtn = [...container.querySelectorAll('.tree-context-menu button')].find((b) => b.textContent === '导出…')
+    await act(async () => { exportBtn?.dispatchEvent(new MouseEvent('click', { bubbles: true })) })
+    expect(onExportEntry).toHaveBeenCalledTimes(1)
+    expect(onExportEntry.mock.calls[0][0].path).toBe('C:/ws/a.md')
+    expect(container.querySelector('.tree-context-menu')).toBeNull()
+    // 再次打开后点别处关闭
+    await act(async () => { rightClick(item) })
+    expect(container.querySelector('.tree-context-menu')).not.toBeNull()
+    await act(async () => { mouseDownOutside() })
+    expect(container.querySelector('.tree-context-menu')).toBeNull()
+    await act(async () => { root.unmount() })
+    container.remove()
+  })
+})