sync-v2 step 1: worker roles + interactive/bulk queue split

- config: WORKER_ROLE (sync|jobs|all), INTERACTIVE_CONCURRENCY, BULK_CONCURRENCY.
- queue: named queues (interactive/bulk) + enqueue_job() router; sync_bootstrap
  goes to bulk, all other jobs to interactive.
- workers.run: single entrypoint; role=jobs runs both arq consumers (per-queue
  timeout/concurrency), role=sync runs the supervisor, all=both (dev default).
- docker-compose: worker-sync + worker-jobs services (shared image, nofile
  ulimit); backend/Dockerfile; Makefile worker/worker-sync/worker-jobs targets.
- tests repointed to app.queue.get_arq_pool; supervisor behavior unchanged.

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

backend/app/outbox/jobs.py

@@ -52,9 +52,7 @@ async def _harvest_recipients(session: AsyncSession, user_id: uuid.UUID, emails:
         await session.execute(stmt)
 
 
-async def _persist_sent_copy(
-    user_id: uuid.UUID, account: Account, raw: bytes, uid: int
-) -> None:
+async def _persist_sent_copy(user_id: uuid.UUID, account: Account, raw: bytes, uid: int) -> None:
     """Store the just-sent message in the DB (Sent mailbox) and notify the UI.
 
     No-op without a UIDPLUS append UID (uid <= 0); in that case a future Sent sync
@@ -64,9 +62,7 @@ async def _persist_sent_copy(
         return
     async with session_scope() as session:
         sent_mb = await session.scalar(
-            select(Mailbox).where(
-                Mailbox.account_id == account.id, Mailbox.special_use == "sent"
-            )
+            select(Mailbox).where(Mailbox.account_id == account.id, Mailbox.special_use == "sent")
         )
         if sent_mb is None:
             return
@@ -99,9 +95,7 @@ async def _persist_sent_copy(
         },
     )
     if thread_id is not None:
-        await bus.publish(
-            "thread.updated", {"user_id": str(user_id), "thread_id": str(thread_id)}
-        )
+        await bus.publish("thread.updated", {"user_id": str(user_id), "thread_id": str(thread_id)})
 
 
 async def send_job(ctx: dict[str, Any], outbox_id: str) -> None: