fix(P0-02): 积分榜改为追加快照(append-only) + available_at cutoff

去掉 uq_standings_league_season_team,改为 (league, season, team, available_at) 唯一;
每次采集 INSERT 新行(available_at=now),ON CONFLICT DO NOTHING,不覆盖旧行。

standings_slice(before):DISTINCT ON (team_id) WHERE available_at<=cutoff
ORDER available_at DESC;before=None → cutoff=now()。
公开 list_standings 取每队最新可用快照(子查询 max available_at)。

迁移 0023 + 切片/路由/docs 同步;测试 test_p0_standings_cutoff(5/5)。
284 测试全绿。

src/data/bzzoiro_standings.py

@@ -137,21 +137,12 @@ async def ingest_bzzoiro_standings(db, *, leagues: Iterable[str], season: str |
                 retrieved_at=now,
             )
 
-            # 同一联赛同一赛季只保留最新快照:按 (league, season, team) upsert
-            stmt = select(Standing).where(
-                Standing.league_id == league.id,
-                Standing.season == season_label,
-                Standing.team_id == team.id,
+            # P0-02: 追加快照——每次采集 INSERT 新行(available_at=now),
+            # ON CONFLICT (league, season, team, available_at) DO NOTHING。
+            standing = Standing(
+                league_id=league.id, season=season_label, team_id=team.id, available_at=now, **values
             )
-            standing = (await db.execute(stmt)).scalar_one_or_none()
-            if standing is None:
-                standing = Standing(
-                    league_id=league.id, season=season_label, team_id=team.id, **values
-                )
-                db.add(standing)
-            else:
-                for k, v in values.items():
-                    setattr(standing, k, v)
+            db.add(standing)
             league_r["upserted"] += 1
 
         league_r["rows"] = len(rows)