[codex] Add JAX oracle witnesses and unified notes

[shinaoka]

Summary

Add the initial unified JAX/PyTorch oracle expansion on top of the existing tensor-ad-oracles layout.

This PR:

• adds JAX witness materialization for published abs/identity and exp/identity cases, including jvp, vjp, linearization, transpose, and adjoint_check
• backfills the published cases/abs/identity.jsonl and cases/exp/identity.jsonl records with jax_ref
• updates replay and regeneration integrity checks so CI validates the JAX witness surface alongside the existing PyTorch oracles
• unifies the math-note structure across published notes and adds README clarification that validate_schema.py is a maintainer/CI integrity tool while published JSONL files already store materialized numeric payloads

Why

The branch extends the current oracle database instead of splitting a separate JAX repository, while making the JAX convention explicit in both the machine-readable witnesses and the math-note corpus.

Validation

• uv run python -m unittest tests.test_repo_config tests.test_scripts tests.test_materialize tests.test_pytorch_v1 tests.test_validator_encoding tests.test_db_replay tests.test_jax_v1 tests.test_runtime_jax tests.test_math_notes_structure tests.test_math_registry -v
• uv run python scripts/verify_cases.py
• uv run python scripts/check_replay.py
• uv run python scripts/check_regeneration.py

Notes

• uv run python scripts/validate_schema.py was measured separately on the current branch and completed successfully in about 6 minutes for 9580 records.