refactor: Sprint 3 - 引入 UnitOfWork + Repository 架构

新增:
- src/db/unit_of_work.py: UnitOfWork 事务封装
- src/db/repositories.py: Match/Team/League/Prediction Repository

重构:
- 删除 src/data/match_lookup.py(由 Repository 替代)
- 数据源(bzzoiro/understat/injuries)不再自行 commit
- API 路由(ingest)改用 UnitOfWork
- LLM 服务(predict/orchestrator/eval/backtest)改用 UnitOfWork

事务边界统一由调用方控制,数据层不再自行决定 commit。

src/llm/agents/orchestrator.py

@@ -11,6 +11,7 @@ from dataclasses import dataclass
 from src.core.config import settings
 from src.db.base import AsyncSessionLocal
 from src.db.models import Match, Prediction
+from src.db.unit_of_work import get_uow
 from src.llm.agents.base import AgentReport, AgentSpec, load_agent_prompt
 from src.llm.context_builder import (
     MatchHeader,
@@ -184,8 +185,9 @@ async def predict_match_multi(
         _reports_to_json(reports).encode("utf-8")
     ).hexdigest()
 
-    # 4. 存库
-    async with AsyncSessionLocal() as db:
+    # 4. 存库(使用 UnitOfWork)
+    async with get_uow() as uow:
+        db = uow.session
         m = await db.get(Match, match_id)
         if m is None:
             raise ValueError(f"match {match_id} not found")
@@ -218,7 +220,7 @@ async def predict_match_multi(
             input_hash=input_hash,
         )
         db.add(pred)
-        await db.commit()
+        await uow.commit()
         await db.refresh(pred)
 
         return MultiPredictResult(