feat: expose bounded M5.2 failure progress

[veil-chow-fyaic]

Summary

• snapshot fixed SQLite aggregate counts before M5.2 scenario cleanup
• derive a conservative failure-stage enum and expose only fixed reconciliation reasons
• reject extra fields, unsafe reasons, impossible counts, and stage/count drift
• update the attempt record, checkpoint, mainline plan, project status, and README validation count

Mainline impact

This converts the next real Codex rerun from a blind retry into a diagnostic run. It does not claim that attempt 11 passed and does not expose prompts, receipts, paths, thread IDs, journals, or arbitrary origin codes.

Validation

• 385/385 unit and subtests
• 55 schema cases
• 7 transition cases
• 114 Markdown files, zero lint issues
• git diff --check

Closes no issue; advances #91.