Add portable PCA transition records and fail-closed validation

[gv1983us-commits]

Summary

• separate a compact portable PCA Core from historical/project profiles
• add a canonical Draft 2020-12 Transition Record schema
• add a stdlib-only fail-closed validator and conformance fixtures
• document corpus verification, MPAA/BEC boundaries, and a concrete resistance corpus
• add CI across Python 3.10–3.13

Safety boundaries

• process continuation does not establish identity, subjectivity, or uninterrupted persistence
• reading a trace is not memory
• external MPAA/BEC conclusions remain carried-not-imported
• unknown state forces an UNDETERMINED overall result
• malformed JSON, duplicate keys, non-finite values, invalid UTF-8, unsupported schema keywords, and temporal contradictions fail closed

Verification

• python -m py_compile validator/*.py
• python -m unittest discover -s validator -p "test_*.py" -v — 31 tests, OK
• 81 canonical-schema comparisons against Draft202012Validator
• 113 additional adversarial mutations — 0 bypasses, 0 crashes
• JSON, relative-link, secret-pattern, local-path, risky-call, and git diff --check scans — clean

Closes #1
Closes #2
Closes #3