Add email sync service for automated job application tracking

Background poller fetches emails via IMAP or Microsoft Graph API,
classifies them with Claude Haiku, and creates/updates JobApplication
records automatically. Includes manual sync endpoint and OAuth callback.

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

backend/handlers/store.go

@@ -18,6 +18,7 @@ type Store struct {
 	Auth          *services.Auth
 	Notes         *services.Notes
 	LoginLimiter  *services.RateLimiter
+	EmailSync     *services.EmailSyncService
 
 	RecentSongs          *[]spotify.RecentlyPlayedItem
 	RecentSongsFetchedAt time.Time