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.ts

@@ -35,6 +35,7 @@ export interface MenuEventHandlers {
   onResolveConflicts?: () => void
   onViewChanges?: () => void
   onInstallMcp?: () => void
+  onReindexVault?: () => void
   activeTabPathRef: React.MutableRefObject<string | null>
   handleCloseTabRef: React.MutableRefObject<(path: string) => void>
   activeTabPath: string | null
@@ -77,7 +78,7 @@ type OptionalHandler =
   | 'onCreateType' | 'onToggleRawEditor' | 'onToggleDiff' | 'onToggleAIChat'
   | 'onOpenVault' | 'onRemoveActiveVault' | 'onRestoreGettingStarted'
   | 'onCreateTheme' | 'onRestoreDefaultThemes'
-  | 'onCommitPush' | 'onResolveConflicts' | 'onViewChanges' | 'onInstallMcp'
+  | 'onCommitPush' | 'onResolveConflicts' | 'onViewChanges' | 'onInstallMcp' | 'onReindexVault'
 
 const OPTIONAL_EVENT_MAP: Record<string, OptionalHandler> = {
   'view-go-back': 'onGoBack',
@@ -96,6 +97,7 @@ const OPTIONAL_EVENT_MAP: Record<string, OptionalHandler> = {
   'vault-resolve-conflicts': 'onResolveConflicts',
   'vault-view-changes': 'onViewChanges',
   'vault-install-mcp': 'onInstallMcp',
+  'vault-reindex': 'onReindexVault',
 }
 
 function dispatchActiveTabEvent(id: string, h: MenuEventHandlers): boolean {