email: set busy_timeout on the email db to ride out concurrent writers

The API and email sidecar both open emails.db; without a busy timeout a write
overlap (resync, or the thread_id backfill) throws "database is locked" and
500s a request. Wait up to 5s for the other writer instead.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/servers/api/email/email-db.ts

@@ -133,6 +133,9 @@ function fallbackThreadId(row: { id: string; subject: unknown; from_address: unk
 export function openEmailDb(email: string): Database {
   const dbPath = join(DATA_PATH, email, 'emails.db');
   const db = new Database(dbPath, { create: true });
+  // The API and the email sidecar both open this file; wait out a concurrent writer (e.g. a resync
+  // or the one-time thread_id backfill) instead of failing immediately with "database is locked".
+  db.exec('PRAGMA busy_timeout = 5000');
   db.exec('PRAGMA journal_mode = DELETE');
   db.exec('PRAGMA foreign_keys = ON');
   db.exec(SCHEMA_TABLES);