fix(postgres-fixture): drop deprecated rules_docker dependency

[ihistand]

Summary

Upstream Dataform removed `@io_bazel_rules_docker` from `WORKSPACE` in commit `8be595ac` (Mar 2024), but the restored Postgres adapter files in `tools/postgres/BUILD` (restored in PR predecessor commit `a220e2ed`) still loaded `container_image` from it, breaking `bazel build //...`:

```
error loading package 'tools/postgres': Unable to find package for
@io_bazel_rules_docker//container:image.bzl: The repository
'@io_bazel_rules_docker' could not be resolved
```

Approach

Two paths considered:

1. Restore @io_bazel_rules_docker in WORKSPACE — ~67 lines of deprecated Bazel infra to maintain.
2. Refactor the fixture to use docker run directly. ← chose this

Modern Postgres LTS, no deprecated Bazel rules, simpler dev flow. PostgresFixture now starts postgres:15-alpine via docker run on the local daemon — no Bazel image staging needed.

Also renamed DOCKER_CONTAINER_NAME from postgres-df-integration-testing → postgres-sa-integration-testing (rename sweep miss).

Verification

./scripts/docker-bazel build -- //... -//tools/postgres/...
# → 332 actions, Build completed successfully

Out of scope

tools/postgres/... itself still doesn't build because the restored adapter imports pg and pg-query-stream, which aren't in package.json. That's Phase 1 of docs/postgres_reintegration_assessment.md — separate PR.

Stack

Stacked on PR #2 (`fix/node-toolchain-pin`). Merge order: #1 → #2 → this.

Test plan

• `./scripts/docker-bazel build -- //... -//tools/postgres/...`
• `./scripts/docker-bazel build //...` (blocked on Postgres adapter Phase 1 — pg / pg-query-stream deps)
• Postgres integration tests against the new `postgres:15-alpine` image (blocked on Phase 1)

🤖 Generated with Claude Code

[ihistand]

Superseded: the Postgres reintegration + Dataform→SQLAnvil rename landed on main directly, and the docs moved to the SQLAnvil/docs repo. Closing as part of #12 (stale-branch prune). The one un-migrated draft, gcp_test_project_setup.md, was migrated to SQLAnvil/docs.