fix(worker): wait for the DB schema before starting (no crash-loop on fresh deploy)

The worker and API start in parallel; the API applies migrations on its own startup, so on a fresh
deploy the worker hit a missing download_jobs table and crash-looped until migrations landed. The
worker now polls for the schema before recovering orphans, and (belt-and-suspenders) the compose
files gate it on the API being healthy. Fixes the observed prod restart-loop on the v0.22.0 deploy.

docker-compose.selfhost.yml

@@ -84,6 +84,10 @@ services:
     depends_on:
       db:
         condition: service_healthy
+      # Start only after the API is healthy (it applies the DB migrations on startup), so the
+      # download tables exist before the worker touches them.
+      api:
+        condition: service_healthy
       bgutil-pot:
         condition: service_started
     networks: [internal]