feat: 添加线索引擎、NLQ、场景检测、前端界面等核心功能模块

backend/app/api/nlq.py

@@ -0,0 +1,24 @@
+"""自然语言查询 API（R4/R20）。"""
+
+from __future__ import annotations
+
+from fastapi import APIRouter, Depends
+from sqlalchemy.orm import Session
+
+from app.api.schemas import NLQRequest, NLQResponse
+from app.db import get_session
+from app.nlq import service as nlq
+
+router = APIRouter(prefix="/nlq", tags=["nlq"])
+
+
+@router.post("", response_model=NLQResponse)
+def ask(req: NLQRequest, session: Session = Depends(get_session)) -> NLQResponse:
+    ans = nlq.ask(req.question, session=session)
+    return NLQResponse(
+        question=ans.question,
+        answer=ans.answer,
+        provider=ans.provider,
+        model=ans.model,
+        egress=ans.egress,
+    )