feat: add Cmd+Shift+T shortcut, menu item, and full wiring

Add "Reopen Closed Tab" to File menu with CmdOrCtrl+Shift+T accelerator.
Wire onReopenClosedTab through useAppKeyboard, useMenuEvents,
useAppCommands, and App.tsx.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/hooks/useMenuEvents.test.ts

@@ -36,6 +36,7 @@ function makeHandlers(): MenuEventHandlers {
     onInstallMcp: vi.fn(),
     onReindexVault: vi.fn(),
     onReloadVault: vi.fn(),
+    onReopenClosedTab: vi.fn(),
     activeTabPathRef: { current: '/vault/test.md' } as React.MutableRefObject<string | null>,
     handleCloseTabRef: { current: vi.fn() } as React.MutableRefObject<(path: string) => void>,
     activeTabPath: '/vault/test.md',
@@ -313,6 +314,13 @@ describe('dispatchMenuEvent', () => {
     expect(h.onReloadVault).toHaveBeenCalled()
   })
 
+  // File menu: reopen closed tab
+  it('file-reopen-closed-tab triggers reopen closed tab', () => {
+    const h = makeHandlers()
+    dispatchMenuEvent('file-reopen-closed-tab', h)
+    expect(h.onReopenClosedTab).toHaveBeenCalled()
+  })
+
   // Edge cases
   it('unknown event ID does nothing', () => {
     const h = makeHandlers()