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/db/models.py

@@ -204,8 +204,11 @@ class MatchStats(Base):
 class Standing(Base):
     """联赛积分榜快照(bzzoiro /leagues/{id}/standings/)。
 
-    同一联赛同一赛季只保留最新快照:重新采集时按 (league_id, season, team_id)
-    upsert。zone 来自 bzzoiro 分区(如 champions_league / europa_league / relegation)。
+    P0-02: 改为追加快照(append-only)。每次采集 INSERT 新行,available_at=now;
+    查询取 available_at<=cutoff 的每队最新快照(DISTINCT ON team_id ORDER available_at DESC)。
+    回测时可还原任意历史时刻的榜单,不再只是"最新快照、忽略 cutoff"。
+    同一 (league_id, season, team_id, available_at) 唯一,ON CONFLICT DO NOTHING。
+    zone 来自 bzzoiro 分区(如 champions_league / europa_league / relegation)。
     """
     __tablename__ = "standings"
 
@@ -228,13 +231,17 @@ class Standing(Base):
     zone: Mapped[str | None] = mapped_column(String(50))  # champions_league / relegation 等
     updated_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=_utcnow, onupdate=_utcnow)
     retrieved_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=_utcnow)
+    # P0-02: 快照可用时间(采集时间),唯一键组成部分 + cutoff 过滤依据
+    available_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), nullable=False, default=_utcnow)
 
     league: Mapped[League] = relationship()
     team: Mapped[Team] = relationship(lazy="selectin")
 
     __table_args__ = (
-        UniqueConstraint("league_id", "season", "team_id", name="uq_standings_league_season_team"),
+        # P0-02: (league, season, team, available_at) 唯一,支持追加快照 + ON CONFLICT DO NOTHING
+        UniqueConstraint("league_id", "season", "team_id", "available_at", name="uq_standings_league_season_team_available"),
         Index("ix_standings_league_season_pos", "league_id", "season", "position"),
+        Index("ix_standings_league_season_team_available", "league_id", "season", "team_id", "available_at"),
     )