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/domain/repositories/selection.py

@@ -10,6 +10,7 @@ from __future__ import annotations
 from datetime import date
 from typing import Protocol
 
+from app.domain.entities.chart import SelectionHit
 from app.domain.entities.selection import SelectionMeta, SelectionResult
 
 
@@ -27,3 +28,6 @@ class SelectionRepository(Protocol):
         limit: int = 20,
     ) -> list[SelectionMeta]:
         """历史选股元数据列表（按 created_at 倒序；可选 as_of/method 过滤）。"""
+
+    def list_by_symbol(self, symbol: str, limit: int = 50) -> list[SelectionHit]:
+        """该股在历史选股中的命中（Chart 标记用，含 as_of/rank/reason）。"""

backend/app/domain/repositories/signal.py

@@ -5,7 +5,7 @@ from __future__ import annotations
 from datetime import date
 from typing import Protocol
 
-from app.domain.entities.signal import SignalMeta, SignalResult
+from app.domain.entities.signal import SignalHit, SignalMeta, SignalResult
 
 
 class SignalRepository(Protocol):
@@ -17,3 +17,6 @@ class SignalRepository(Protocol):
     def list_recent(
         self, as_of: date | None = None, limit: int = 20
     ) -> list[SignalMeta]: ...
+
+    def list_by_symbol(self, symbol: str, limit: int = 50) -> list[SignalHit]:
+        """该股在历史信号中的命中（Chart 标记用，含 signal_id 溯源）。"""