Draft: Add hybrid CASE_HASH support for issue #136

[tomvothecoder]

Summary

• parse and persist CASE_HASH from env_case.xml
• keep case-name-based grouping as the authoritative resolver
• warn when CASE_HASH drifts across executions for the same case name
• expose case_hash on simulation schemas and add a migration for simulations.case_hash

Why not group by CASE_HASH yet?

Issue #136 now has confirmed real-world evidence that CASE_HASH can be consistent across some executions and drift across others for the same logical case. Making it the sole grouping key now would risk splitting one logical case into multiple SimBoard cases.

This change implements the safe hybrid path:

• store CASE_HASH
• make it available for diagnostics and future evaluation
• retain existing case-name grouping when hashes conflict or are missing

Testing

• uv run pytest tests/features/ingestion/parsers/test_case_docs.py tests/features/ingestion/test_ingest.py tests/features/simulation/test_schemas.py tests/features/simulation/test_api.py
• make backend-test

Refs #136