- Add tkRestrict token to lexer
- Parse ON DELETE CASCADE/SET NULL/RESTRICT and ON UPDATE CASCADE/SET NULL/RESTRICT
in both table-level and column-level FK constraints
- Add fkOnDelete/fkOnUpdate to ColumnDef and ForeignKeyDef
- Fix table-level FK constraint application (third pass after columns are created)
- Implement enforceFkOnDelete, enforceFkOnUpdate, enforceFkOnChildUpdate helpers
- Wire FK enforcement into DELETE and UPDATE execution paths
- Add 9 regression tests covering all FK actions