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/useCommandRegistry.test.ts

@@ -95,6 +95,46 @@ describe('useCommandRegistry', () => {
     expect(cmd!.enabled).toBe(false)
   })
 
+  it('includes reindex-vault command in Settings group', () => {
+    const config = makeConfig({ onReindexVault: vi.fn() })
+    const { result } = renderHook(() => useCommandRegistry(config))
+    const cmd = findCommand(result.current, 'reindex-vault')
+    expect(cmd).toBeDefined()
+    expect(cmd!.group).toBe('Settings')
+    expect(cmd!.label).toBe('Reindex Vault')
+  })
+
+  it('reindex-vault is enabled when onReindexVault is provided', () => {
+    const config = makeConfig({ onReindexVault: vi.fn() })
+    const { result } = renderHook(() => useCommandRegistry(config))
+    const cmd = findCommand(result.current, 'reindex-vault')
+    expect(cmd!.enabled).toBe(true)
+  })
+
+  it('reindex-vault is disabled when onReindexVault is not provided', () => {
+    const config = makeConfig()
+    const { result } = renderHook(() => useCommandRegistry(config))
+    const cmd = findCommand(result.current, 'reindex-vault')
+    expect(cmd!.enabled).toBe(false)
+  })
+
+  it('reindex-vault executes onReindexVault callback', () => {
+    const onReindexVault = vi.fn()
+    const config = makeConfig({ onReindexVault })
+    const { result } = renderHook(() => useCommandRegistry(config))
+    const cmd = findCommand(result.current, 'reindex-vault')
+    cmd!.execute()
+    expect(onReindexVault).toHaveBeenCalled()
+  })
+
+  it('reindex-vault has searchable keywords', () => {
+    const config = makeConfig({ onReindexVault: vi.fn() })
+    const { result } = renderHook(() => useCommandRegistry(config))
+    const cmd = findCommand(result.current, 'reindex-vault')
+    expect(cmd!.keywords).toContain('reindex')
+    expect(cmd!.keywords).toContain('search')
+  })
+
   it('resolve-conflicts stays enabled across rerenders', () => {
     const config = makeConfig()
     const { result, rerender } = renderHook(