feat: 添加回测框架

- 新增 src/llm/backtest.py: 回测核心逻辑
  - 查询历史已完赛比赛
  - 逐场预测(自动防未来信息泄漏)
  - 实际比分回填 + 统计
  - 1X2 准确率 / 比分 RMSE / 置信度校准
- 新增 POST /api/v1/backtest 路由
- 支持按联赛/日期范围/模式/模型筛选

src/api/app.py

@@ -41,11 +41,13 @@ def create_app() -> FastAPI:
     from src.api.routes.predict import router as predict_router
     from src.api.routes.ingest import router as ingest_router
     from src.api.routes.eval import router as eval_router
+    from src.api.routes.backtest import router as backtest_router
 
     app.include_router(matches_router)
     app.include_router(predict_router)
     app.include_router(ingest_router)
     app.include_router(eval_router)
+    app.include_router(backtest_router)
 
     @app.get("/health")
     async def health():