The test job failed on the runner with:
Bind for 0.0.0.0:27017 failed: port is already allocated
because the services.mongo ports: 27017:27017 tries to claim host port
27017, which is occupied (mongod on the runner host). The job container
doesn't need the host mapping — it reaches Mongo over the job's internal
network via the service hostname (MONGODB_URI=mongodb://mongo:27017).
Drop the ports block so the service container schedules cleanly.
This unblocks all PRs, including #6 (Phase A1).
