fix: harden commit-semantic follow-up

[feng-y]

Summary

• harden the commit-semantic LLM trust boundary by rejecting unknown classification domains and malformed IDs
• make SHA-to-file-path parsing delimiter-safe and align repo-structure hotspot consumption with the actual commit-semantic aggregate schema
• update top-level release documentation to reflect the new commit-extract / commit-semantic pipeline and runtime contract

Test plan

• pytest tests/test_commit_semantic_domain.py tests/e2e/test_commit_semantic.py tests/test_repo_structure.py -q
• pytest tests -q
• ruff check .

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