Archive completed reviews and retain deferred TODOs

[bonelifer]

Summary

• Preserve four historical Codex and AI validation reports in the numbered TODO archive.
• Add a TODO index, retain the deferred informational findings and repair report links.
• Link the TODO index from the README. No extension behavior changes.

Test plan

• Codex checked the documentation-only diff with git diff --check.
• Archived reports retain their original findings; archiving does not certify a fresh review.

cc @kaileymsnay

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Investigated and written by Codex on behalf of William Jacoby (bonelifer).