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>

docker/docker-compose.yml

@@ -36,6 +36,36 @@ services:
       timeout: 3s
       retries: 10
 
+  # Sync-engine v2 workers (refactor §1): two roles sharing one image. Scale the
+  # sync role with `--scale worker-sync=N` (lease protocol prevents double-owning).
+  worker-sync:
+    build: { context: ../backend }
+    command: ["python", "-m", "workers.run"]
+    environment: &worker-env
+      WORKER_ROLE: sync
+      APP_DOMAIN: dev.webmail.local
+      DATABASE_URL: postgresql+asyncpg://webmail:webmail_dev@postgres:5432/webmail_dev
+      REDIS_URL: redis://redis:6379/0
+      MASTER_KEY: CHANGE_ME_base64_32_bytes
+      BLOB_ROOT: /var/blobs
+    volumes: [blobs:/var/blobs]
+    ulimits: { nofile: 65536 }
+    depends_on:
+      postgres: { condition: service_healthy }
+      redis: { condition: service_healthy }
+
+  worker-jobs:
+    build: { context: ../backend }
+    command: ["python", "-m", "workers.run"]
+    environment:
+      <<: *worker-env
+      WORKER_ROLE: jobs
+    volumes: [blobs:/var/blobs]
+    ulimits: { nofile: 65536 }
+    depends_on:
+      postgres: { condition: service_healthy }
+      redis: { condition: service_healthy }
+
   # Test mail servers (integration tests + manual dev against a throwaway mailbox)
   greenmail:
     image: greenmail/standalone:2.0.1
@@ -51,3 +81,4 @@ services:
 volumes:
   pgdata:
   meilidata:
+  blobs: