Add ORM migration foundation

[shiny-code-bot]

Summary

• add Alembic migration infrastructure and a baseline revision for the current Launchplane SQLAlchemy schema
• document the ORM query boundary, field-promotion audit, JSONB evidence rule, and existing DB stamp posture
• add lane and preview summary read models plus repository methods for GUI-facing storage reads

Verification

• python3 -m py_compile control_plane/contracts/lane_summary.py control_plane/contracts/preview_summary.py control_plane/storage/postgres.py control_plane/storage/migrations/env.py control_plane/storage/migrations/versions/fe94a0486977_baseline_current_schema.py
• uv run ruff check control_plane/contracts/lane_summary.py control_plane/contracts/preview_summary.py control_plane/storage/postgres.py tests/test_postgres_store.py
• uv run ruff format --check control_plane/contracts/lane_summary.py control_plane/contracts/preview_summary.py control_plane/storage/postgres.py tests/test_postgres_store.py
• uv run python -m unittest discover -s tests

Notes

• Existing live databases created by the pre-Alembic create_all path should be table-shape checked and then stamped with alembic stamp head before future schema migrations.
• Driver action availability is intentionally left for the provider-neutral driver descriptor/action contract slice.