feat: complete commit-semantic domain pipeline

[feng-y]

Summary

• complete the domain-based commit-semantic pipeline and align commit-extract / repo-structure integrations with the new JSONL contract
• switch commit-semantic to LLM-only discover/classify with truthful runtime provenance and host-executor orchestration support
• add spec, gstack implementation plan, and comprehensive regression / e2e coverage for normalization, classification, provenance, and real model-in-the-loop flow

Test plan

• pytest tests/test_commit_semantic_domain.py tests/e2e/test_commit_semantic.py tests/test_export_dataclasses.py -q
• pytest tests -q
• ruff check .
• real repo commit-semantic run verified in LLM-only mode with model-in-the-loop orchestration

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