chore: upload app/llm/__init__.py

app/llm/__init__.py

@@ -0,0 +1,5 @@
+"""LLM provider 抽象. 由 factory.py 根据 settings.llm_provider 选择."""
+from app.llm.base import AbstractLLM, LLMChunk, LLMMessage
+from app.llm.factory import get_llm
+
+__all__ = ["AbstractLLM", "LLMChunk", "LLMMessage", "get_llm"]