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/api/router.py

@@ -10,6 +10,7 @@ from fastapi import APIRouter
 
 from app.api import (
     agent,
+    charts,
     composites,
     experiments,
     factors,
@@ -29,6 +30,7 @@ api_router.include_router(factors.router)
 api_router.include_router(composites.router)
 api_router.include_router(research.router)
 api_router.include_router(selections.router)
+api_router.include_router(charts.router)
 api_router.include_router(signals.router)
 api_router.include_router(strategies.router)
 api_router.include_router(jobs.router)