feat: add Check for Updates command to native menu and Cmd+K palette

- Add APP_CHECK_FOR_UPDATES constant and menu item in menu.rs (between About and Settings)
- Wire onCheckForUpdates handler through useMenuEvents and useAppCommands
- Add test for app-check-for-updates dispatch

src/hooks/useAppCommands.ts

@@ -122,6 +122,7 @@ export function useAppCommands(config: AppCommandsConfig): CommandAction[] {
     onSearch: config.onSearch,
     onGoBack: config.onGoBack,
     onGoForward: config.onGoForward,
+    onCheckForUpdates: config.onCheckForUpdates,
     activeTabPathRef: config.activeTabPathRef,
     handleCloseTabRef: config.handleCloseTabRef,
     activeTabPath: config.activeTabPath,

src/hooks/useMenuEvents.test.ts

@@ -19,6 +19,7 @@ function makeHandlers(): MenuEventHandlers {
     onSearch: vi.fn(),
     onGoBack: vi.fn(),
     onGoForward: vi.fn(),
+    onCheckForUpdates: 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',
@@ -161,6 +162,12 @@ describe('dispatchMenuEvent', () => {
     expect(h.onGoForward).toHaveBeenCalled()
   })
 
+  it('app-check-for-updates triggers check for updates', () => {
+    const h = makeHandlers()
+    dispatchMenuEvent('app-check-for-updates', h)
+    expect(h.onCheckForUpdates).toHaveBeenCalled()
+  })
+
   it('unknown event ID does nothing', () => {
     const h = makeHandlers()
     dispatchMenuEvent('unknown-event', h)

src/hooks/useMenuEvents.ts

@@ -19,6 +19,7 @@ export interface MenuEventHandlers {
   onSearch: () => void
   onGoBack?: () => void
   onGoForward?: () => void
+  onCheckForUpdates?: () => void
   activeTabPathRef: React.MutableRefObject<string | null>
   handleCloseTabRef: React.MutableRefObject<(path: string) => void>
   activeTabPath: string | null
@@ -58,6 +59,7 @@ function dispatchActiveTabEvent(id: string, h: MenuEventHandlers): boolean {
 function dispatchOptionalEvent(id: string, h: MenuEventHandlers): boolean {
   if (id === 'view-go-back') { h.onGoBack?.(); return true }
   if (id === 'view-go-forward') { h.onGoForward?.(); return true }
+  if (id === 'app-check-for-updates') { h.onCheckForUpdates?.(); return true }
   return false
 }