feat(chart): M9-1 Chart DTO + Chart Service + Chart API（v3 §20）

- domain/entities/chart.py：ChartResult/OHLC/Volume/Series/EventMarker/ChartMetadata
  （adjust_mode + execution_price_basis 口径元数据）+ SelectionHit
- application/services/chart_service.py：个股 K线/量/MA 指标；显示层 qfq/hfq 折算
  （基于主口径 none 行情 × adjust_factor，绝回写研究数据）；回测个股视图把实际成交
  转 fills 标记并在显示口径不同时做坐标换算（v3 §20.3/§20.5）
- by-symbol 历史查询：SignalRepository/SelectionRepository.list_by_symbol（含溯源 id）
- api/charts.py：/stocks/{symbol}/chart|signals|selections、/backtests/{id}/stocks/{symbol}/chart
  |trades|positions
- tests/test_charts.py（指标/qfq-hfq 折算断言/回测 fills/API 集成+404）；全量 pytest 通过

backend/app/infrastructure/persistence/sqlalchemy/repositories/selection_impl.py

@@ -12,6 +12,7 @@ from datetime import date, datetime
 from sqlalchemy import select
 from sqlalchemy.orm import Session
 
+from app.domain.entities.chart import SelectionHit
 from app.domain.entities.selection import (
     SelectionCandidate,
     SelectionMeta,
@@ -84,6 +85,27 @@ class SqlAlchemySelectionRepository:
             config_snapshot=json.loads(snap.query_json),
         )
 
+    def list_by_symbol(self, symbol: str, limit: int = 50) -> list[SelectionHit]:
+        rows = self._session.execute(
+            select(SelectionResultModel, SelectionSnapshotModel.as_of, SelectionSnapshotModel.method)
+            .join(SelectionSnapshotModel, SelectionSnapshotModel.id == SelectionResultModel.selection_id)
+            .where(SelectionResultModel.symbol == symbol)
+            .order_by(SelectionSnapshotModel.as_of.desc(), SelectionResultModel.rank)
+            .limit(limit)
+        ).all()
+        return [
+            SelectionHit(
+                selection_id=r[0].selection_id,
+                as_of=r[1],
+                method=r[2],
+                symbol=r[0].symbol,
+                rank=r[0].rank,
+                score=float(r[0].score),
+                selection_reason=json.loads(r[0].reason_json or "[]"),
+            )
+            for r in rows
+        ]
+
     def list_recent(
         self,
         as_of: date | None = None,