Refactor _resolve_matching_subtype to use an LLM agent for ambiguous
cases instead of pure static rules:
Architecture (3 layers):
1. Static deterministic rules: M:N→MxN, 1:N (WS-MAST/TRAN-KEY),
二段階, 混合 — high confidence, no LLM needed
2. LLM agent: ambiguous cases (N:1 vs 1:1, M:N→M vs M:N→N)
- _MATCHING_SUBTYPE_AGENT_PROMPT with 5 subtypes
- Calls existing hina.hina_agent._parse_llm_response for parsing
- Minimum confidence threshold 0.4 to gate low-quality LLM output
3. Fallback: conservative defaults (M:N or 1:1) when LLM unavailable
This follows the original architecture design: agent handles the
hard classification problems that static analysis alone can't resolve.
Regression: 745 passed (unchanged).
NB-076
6b3f526b80