Persist runner host hygiene audits

[cbusillo]

Summary

• add Launchplane-owned filesystem and Postgres storage for runner-host hygiene audit records
• add an Alembic migration for launchplane_runner_host_hygiene_audits, including idempotent upgrade behavior for stamped schemas that already have the ORM-created table
• document the audit record family and cover storage/import round trips

Validation

• uv run python -m unittest tests.test_filesystem_store tests.test_postgres_store
• uv run --extra dev ruff check control_plane/storage/filesystem.py control_plane/storage/postgres.py control_plane/storage/migrations/versions/c3e5f7a9b1d2_add_runner_host_hygiene_audits.py tests/test_filesystem_store.py tests/test_postgres_store.py
• uv run --extra dev ruff format --check control_plane/storage/filesystem.py control_plane/storage/postgres.py control_plane/storage/migrations/versions/c3e5f7a9b1d2_add_runner_host_hygiene_audits.py tests/test_filesystem_store.py tests/test_postgres_store.py
• uv run --extra dev mypy control_plane/storage/filesystem.py control_plane/storage/postgres.py control_plane/storage/migrations/versions/c3e5f7a9b1d2_add_runner_host_hygiene_audits.py tests/test_filesystem_store.py tests/test_postgres_store.py
• git diff --check
• JetBrains inspection, changed files: clean

Refs #474