Add PostgreSQL AI Hacking Tools documentation

Create REV/CLAUDE.md with comprehensive subagents and workflows for
AI-assisted PostgreSQL patch development. This includes:

- 15 specialized subagents covering the full patch lifecycle:
  - Building and testing (pg-build, pg-test, pg-benchmark)
  - Code quality (pg-style, pg-review, pg-coverage)
  - Patch management (pg-patch-create, pg-patch-version, pg-patch-apply)
  - Communication (pg-hackers-letter, pg-commitfest, pg-feedback)
  - Documentation and debugging (pg-docs, pg-debug)
  - Final validation (pg-readiness)

- Complete workflows for new features, bug fixes, and patch review
- Critical human checkpoints that cannot be automated
- Common pitfalls and how to avoid them
- References to official PostgreSQL development resources

Based on research of recent pgsql-hackers discussions and the
CommitFest process at commitfest.postgresql.org.

Author: claude