Validate observed upstream schemas during static builds

[tiankaima]

Summary

• profile raw curriculum JSON before Pydantic validation and compare observed shapes with the expected Pydantic contract
• fail on soundness drift while treating incomplete nullability/union evidence as bounded diagnostics
• report unnecessary optional fields only after complete or repeated independent observations
• keep observed reports local/CI-only and publish expected schemas as the public build artifact
• make model validation strict and preserve atomic rollback for schema failures

Verification

• uv run ruff format --check .
• uv run ruff check .
• uv run python -m unittest discover -s tests (57 passed)
• real incremental static load validated catalog plus 21 JW chunks; the upstream later timed out and the build rolled back atomically