feat(replay): M9-6 Bar Replay 线性重放（as_of 逐日仅用当时数据）

- domain/entities/replay.py：ReplayDay{top/events/counts}/ReplayResult 时间线
- ReplayService：universe.symbols 白名单必填（≤40）且重放交易日 ≤90（防全市场长任务）；
  每个交易日以 <=as_of 数据经同一 signal/score 引擎生成帧
- POST /api/replays（边界校验）→ 时间线；供前端 Bar Replay 控件（v3 §20.6 阶段二）
- tests/test_replays.py：重放帧 == 回测 selection_history 逐调仓日一致；范围约束；
  后段暴涨股不泄漏进早段帧（未来函数）；API 400/200；全量 pytest 通过

backend/app/api/replays.py

@@ -0,0 +1,33 @@
+"""Bar Replay API（M9-6）：POST /api/replays —— 线性重放选股/信号时间线。"""
+
+from __future__ import annotations
+
+from datetime import date
+
+from fastapi import APIRouter, HTTPException
+from pydantic import BaseModel, Field
+
+from app.api.deps import ReplayServiceDep
+from app.domain.entities.replay import ReplayResult
+from app.domain.entities.selection import SelectionQuery
+from app.domain.entities.signal import SignalRules
+
+router = APIRouter(prefix="/replays", tags=["replays"])
+
+
+class ReplayRequest(BaseModel):
+    query: SelectionQuery
+    rules: SignalRules = SignalRules()
+    start: date
+    end: date
+    top_n: int = Field(default=5, ge=1, le=20)
+
+
+@router.post("", response_model=ReplayResult, summary="线性重放（as_of 逐日，仅用当时数据）")
+def run_replay(req: ReplayRequest, service: ReplayServiceDep) -> ReplayResult:
+    if req.start >= req.end:
+        raise HTTPException(status_code=400, detail="start 必须早于 end")
+    try:
+        return service.replay(req.query, req.rules, req.start, req.end, req.top_n)
+    except ValueError as exc:
+        raise HTTPException(status_code=400, detail=str(exc)) from exc