#3 feat(db): provision Postgres and add score schema migration

Wire in the txt_game_scores database provision and create the
players/games tables via a provision-scoped migration so Child 2
can implement the server-side score persistence.

- module.yml: requires postgres database (txt_game_scores) with
  env_map for host/port/user/password/name; empty env keys added
  so env-sync populates them after provisioning
- migrations/package.json: ESM, pg + typescript devdeps
- migrations/provision/postgres/000-init-scores.ts: creates
  players and games tables with idempotent IF NOT EXISTS guards
  and two supporting indexes (scoreboard sort, history lookup)

Server code, Dockerfile, and docker-compose.yml are unchanged —
server integration is deferred to the follow-on child task.

Task: 3dab55e3-9792-47a0-a4a6-ba7757517314