replace imap gmail sync with mbsync + maildir import, app password UI

- rewrite gmail-sync handler: mbsync downloads to local Maildir, then import to sqlite
- add app password field to google integration config and API
- gmail sync section independent from oauth in settings UI
- live mbsync progress streaming to job status
- recoverable failure email with instructions for overquota/auth errors
- sync meta persisted to job on failure for richer notifications

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

src/servers/data-path.ts

@@ -93,6 +93,8 @@ export const getAttachmentsDir = (email: string, provider: 'claude' | 'opencode'
 
 export const getUserEmailDir = (email: string) => join(DATA_PATH, email, 'Gmail', 'emails');
 
+export const getMaildirPath = (email: string) => join(DATA_PATH, email, 'Gmail', 'Maildir');
+
 /** Derive a valid Linux username from a display username or email. */
 export const toShellUsername = (username: string, email: string): string => {
   const raw = username || email.split('@')[0]!;