Tenant schemas were never migrated when new migrations were deployed.
Only the public schema was migrated at startup, and tenant schemas only
got migrations when first provisioned. This meant existing tenants
missed any new columns (e.g. task_payload, worker_id, claimed_at on
async_operations), causing the worker poller to crash silently.
Changes:
- Run migrations on all existing tenant schemas at startup when a
tenant_extension is configured. Each schema migration is wrapped in
try/except so one failure doesn't block others.
- Add try/except in WorkerPoller.recover_own_tasks() so a broken
schema doesn't prevent the polling loop from starting.
- Add try/except in WorkerPoller._claim_batch_for_schema() so a
broken schema doesn't prevent claiming tasks from other schemas.