Add local pytest integration tests for the targetDB CI workflow

[monodera]

Summary

• Add a Docker-backed pytest suite (tests/integration/) that reproduces the same pfs-targetdb-cli sequence as .github/workflows/test_database.yml (create-db → q3c → schema → insert example data → prep-fluxstd → transfer/insert targets → insert-pointings → update-catalog-active), so it can be run and debugged locally without pushing to GitHub.
• Unlike the CI job, which only checks command exit codes, the new tests verify the inserted data with SQL (row counts vs. source CSV/ECSV files, foreign-key linkage, rename-cols behavior, active-flag scoping).
• tests/docker/ provides a dedicated postgres:16 + Q3C image and compose file (tmpfs data dir, isolated port 15433) so the suite never touches a developer's existing Postgres/examples/docker/ setup.
• Integration tests are auto-skipped with a clear reason when Docker isn't available, and a --keep-db flag leaves the container running for post-failure inspection.
• .github/workflows/test_database.yml is unchanged; this is a local-only addition for now.

Test plan

• uv run pytest tests -v → 22 passed, 1 skipped
• uv run pytest tests -m "not integration" → integration tests deselected, unit tests still run
• With docker removed from PATH → all integration tests skip with an explanatory reason; unit tests still pass
• uv run pytest tests/integration -v --keep-db → container stays up and reachable afterwards; manually torn down with docker compose -f tests/docker/docker-compose.test.yml down -v
• docker ps -a / docker volume ls show no leftover resources after a normal run
• git status clean after a run — examples/data/ is never written to (all generated files go to a pytest tmp dir)

🤖 Generated with Claude Code