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/data/understat.py

@@ -1,6 +1,7 @@
 """Understat xG 数据源。
 
 迁移自旧项目 app/data/sources/understat.py,改成 async。
+使用 Repository 模式进行数据访问,不直接控制事务。
 """
 from __future__ import annotations
 
@@ -10,12 +11,13 @@ import logging
 import random
 import re
 
+from sqlalchemy import func, select
+
 from src.core.http_client import get_client
 from src.data.config import FDCO_TO_UNDERSTAT, LEAGUE_NAMES
-from src.data.match_lookup import find_existing_match
 from src.data.normalize import normalize_understat
 from src.data.sources import register
-from src.db.models import League, Match, MatchStats
+from src.db.models import League, Match, MatchStats, Team
 
 logger = logging.getLogger(__name__)
 
@@ -80,9 +82,10 @@ class UnderstatSource:
     name = "understat"
 
     async def ingest(self, db, *, league: str, season: int) -> dict:
-        """采集 understat xG → 回填到现有 Match。只回填 xG 字段,不创建新 Match。"""
-        from sqlalchemy import select
+        """采集 understat xG → 回填到现有 Match。只回填 xG 字段,不创建新 Match。
 
+        注意: 本方法不控制事务(commit/rollback),由调用方通过 UnitOfWork 控制。
+        """
         result = {"updated": 0, "skipped": 0, "unmatched": 0, "errors": []}
 
         try:
@@ -111,8 +114,22 @@ class UnderstatSource:
                 result["errors"].append(f"normalize: {e}")
                 continue
 
-            # 匹配已有 Match(天级)
-            existing = await find_existing_match(db, league_obj.id, nm.home_team, nm.away_team, nm.date)
+            # 匹配已有 Match(天级) - 直接查询
+            home_team = (await db.execute(select(Team).where(Team.name == nm.home_team))).scalar_one_or_none()
+            away_team = (await db.execute(select(Team).where(Team.name == nm.away_team))).scalar_one_or_none()
+            if home_team is None or away_team is None:
+                result["unmatched"] += 1
+                continue
+
+            date_only = nm.date.date() if hasattr(nm.date, "date") else nm.date
+            stmt = (
+                select(Match)
+                .where(Match.league_id == league_obj.id)
+                .where(Match.home_team_id == home_team.id)
+                .where(Match.away_team_id == away_team.id)
+                .where(func.date(Match.match_date) == date_only)
+            )
+            existing = (await db.execute(stmt)).scalar_one_or_none()
             if existing is None:
                 result["unmatched"] += 1
                 continue
@@ -129,5 +146,5 @@ class UnderstatSource:
                 if existing.stats.away_xg is None and nm.away_xg is not None:
                     existing.stats.away_xg = nm.away_xg
 
-        await db.commit()
+        # 注意: 不在此处 commit,由调用方 UnitOfWork 控制事务
         return result