Fix SQLAlchemy auto-correlation bug in vestigingen reader + add reader tests

[rverk]

Summary

• Fix runtime crash in get_outdated_vestigingen_count() and get_outdated_vestigingen(): the exists() subquery referenced VestigingenORM, which also appears in the outer query JOIN — SQLAlchemy auto-correlated it by dropping VestigingenORM from the subquery's FROM clause. Fixed with .correlate(BasisProfielORM).
• Add tests/db/test_kvkvestigingen_reader.py (18 tests) and tests/db/test_vestigingsprofiel_reader.py (21 tests) — integration tests that execute queries against SQLite, which would have caught this bug before merge.

Root cause

# Both the outer query and the subquery reference VestigingenORM.
# SQLAlchemy removes it from the subquery's FROM clause → empty FROM → crash.
blocked = (
    exists()
    .where(VestigingenORM.kvk_nummer == BasisProfielORM.kvk_nummer)
    ...
    .correlate(BasisProfielORM)  # ← fix: only correlate with BasisProfielORM
)

No database migration needed

No schema changes — only query logic and new tests.

Test plan

• just check-all passes (run twice)
• Vestigingen app cycles without the "returned no FROM clauses" error
• KVK nummers with IPD0005/IPD1002 still blocked correctly in subsequent cycles

🤖 Generated with Claude Code