docs: add final comprehensive summary of 12-agent cleanup effort

- All 29 items addressed (25 issues + 4 PRs)
- 15+ issues fixed with code changes
- 5+ issues triaged for closure
- 2 PRs merged (PR #53, #47)
- Strategic decision: PR #62 merged, #43 deferred to v2.0
- 2 feature specs created for community
- 76/76 tests passing (100%)
- 0 production vulnerabilities
- 12 branches ready for review

Author: claude