Remove downstream execution audit automation

[Pigbibi]

Summary

• remove recurring monthly execution audit, AI review, auto-optimization, and experiment-validation workflows
• delete the now-unused audit/optimization scripts and tests
• update docs, Makefile, and CI compile list to keep BinancePlatform focused on runtime execution only
• refresh the runtime workflow config smoke test for OIDC instead of the removed GCP_SA_KEY secret

Verification

• git diff --check
• python -m py_compile for CI compile targets
• bash tests/test_runtime_workflow_shared_config.sh
• python -m unittest discover -s tests -v (local dependency-limited: import failures for numpy, pandas, and crypto_strategies because this VPS environment does not have CI dependencies installed)