feat: reindex vault command, indexing status bar, sync-triggered reindex

- Add "Reindex Vault" command to command palette and menu bar
- Show "Indexed Xm ago" in status bar when idle, clickable to reindex
- After git pull with updates, auto-trigger incremental reindex
- Add lastIndexedTime state to useIndexing, populated from backend metadata
- Add triggerFullReindex to useIndexing (retryIndexing is now an alias)
- Add onSyncUpdated callback to useAutoSync
- Extract formatIndexedElapsed to utils/indexingHelpers.ts
- Tests: 20 new unit tests across 5 files, 2 Playwright smoke tests

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

src/hooks/useMenuEvents.test.ts

@@ -34,6 +34,7 @@ function makeHandlers(): MenuEventHandlers {
     onResolveConflicts: vi.fn(),
     onViewChanges: vi.fn(),
     onInstallMcp: vi.fn(),
+    onReindexVault: 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',
@@ -299,6 +300,12 @@ describe('dispatchMenuEvent', () => {
     expect(h.onInstallMcp).toHaveBeenCalled()
   })
 
+  it('vault-reindex triggers reindex vault', () => {
+    const h = makeHandlers()
+    dispatchMenuEvent('vault-reindex', h)
+    expect(h.onReindexVault).toHaveBeenCalled()
+  })
+
   // Edge cases
   it('unknown event ID does nothing', () => {
     const h = makeHandlers()