gmail sync: don't retry on overquota, import what we have

- OVERQUOTA from Gmail now continues to import step instead of retrying
- partial sync completion email tells user to try again in a few hours
- engine syncs handler meta to job on completion for richer notifications

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

src/servers/queue/engine.ts

@@ -218,6 +218,7 @@ async function runJob(job: Job) {
   if (final && final.status === 'running') {
     final.status = 'completed';
     final.completedAt = Date.now();
+    final.meta = { ...final.meta, ...sharedMeta };
     await writeJob(final);
     console.log(`[queue] Job ${final.id} completed`);
     if (final.notify !== false) await notifyCompletion(final);