docs: implementation plan for pre-flight migration review

Six TDD tasks. Records the JSqlParser 5.2 finding that NOT VALID and
CREATE INDEX CONCURRENTLY fail to parse — the safe forms this tool
recommends — and the verified normalization shim that fixes it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: notSumit25