## Problem
`go test ./...` leaked one Docker volume per test package. `pgtest.Main` tore its throwaway container down with `docker rm -f` — no `-v`. The `postgres:17-alpine` image declares a `VOLUME` for `/var/lib/postgresql/data`, and an explicit `rm` without `-v` orphans that anonymous volume even though the container was created with `--rm`.
Found in passing: a 13-hour-old orphaned pgtest container (AutoRemove, `fsync=off`, one mount) still running from a killed test binary — the same leak's other half. Removed on the dev machine.
## Change
- `backend/internal/pgtest/pgtest.go`: `-v` on all three `docker rm -f` teardown sites (`Main`'s defer, and both error paths in `start`).
- `AGENTS.md`: cleanup expectation under Commands — `docker compose down -v` for a stack, `docker rm -f -v` for a hand-run container, then check `docker volume ls` and `docker system df`. Explicitly out of bounds: removing the user's `postgres-data` volume, or a blanket `docker system prune` of their images and build cache.
## Verification
`docker volume ls` snapshot diffed across a real `./internal/store` run: no new volumes, `docker system df` reports 0 local volumes.
Reviewed-on: #175
Co-authored-by: Sulthan Zaki <sultankiki05@gmail.com>
Co-committed-by: Sulthan Zaki <sultankiki05@gmail.com>
sulthan
e1ba7fdabb