feat(strategy): M8.3 策略模型 + /api/strategies（命名配置资产，可展开为 ResearchSpec）

- StrategyDefinition：universe/factors/selection/rebalance/costs/portfolio +
  price_adjustment（除 period 外完整策略定义）；to_research_spec(period) 展开为标准 Spec
- strategy 表（migration e1f2a3b4c5d6，MySQL 已应用；name 唯一）+ StrategyRepository
- /api/strategies：POST/GET/DELETE + POST /{id}/expand（period+initial_capital → ResearchSpec）
- tests/test_strategies.py（repo CRUD/同名/expand、API CRUD/400/404）；全量 pytest 通过

backend/app/api/deps.py

@@ -22,6 +22,7 @@ from app.domain.repositories.market import (
 )
 from app.domain.repositories.selection import SelectionRepository
 from app.domain.repositories.signal import SignalRepository
+from app.domain.repositories.strategy import StrategyRepository
 from app.infrastructure.persistence.sqlalchemy.repositories.composite_impl import (
     SqlAlchemyCompositeRepository,
 )
@@ -39,6 +40,9 @@ from app.infrastructure.persistence.sqlalchemy.repositories.selection_impl impor
 from app.infrastructure.persistence.sqlalchemy.repositories.signal_impl import (
     SqlAlchemySignalRepository,
 )
+from app.infrastructure.persistence.sqlalchemy.repositories.strategy_impl import (
+    SqlAlchemyStrategyRepository,
+)
 from app.infrastructure.persistence.sqlalchemy.session import get_session
 from app.quant.engine import LocalEngine, QuantEngine
 from app.quant.service import ResearchService
@@ -102,6 +106,10 @@ def _signal_repo_factory(session: DbSession) -> SignalRepository:
     return SqlAlchemySignalRepository(session)
 
 
+def _strategy_repo_factory(session: DbSession) -> StrategyRepository:
+    return SqlAlchemyStrategyRepository(session)
+
+
 StockRepoDep = Annotated[StockRepository, Depends(_stock_repo_factory)]
 DailyRepoDep = Annotated[DailyBarRepository, Depends(_daily_repo_factory)]
 EngineDep = Annotated[QuantEngine, Depends(_engine_factory)]
@@ -112,6 +120,7 @@ FactorRepoDep = Annotated[FactorRepository, Depends(_factor_repo_factory)]
 CompositeRepoDep = Annotated[CompositeRepository, Depends(_composite_repo_factory)]
 SignalRepoDep = Annotated[SignalRepository, Depends(_signal_repo_factory)]
 SignalServiceDep = Annotated[SignalService, Depends(_signal_service_factory)]
+StrategyRepoDep = Annotated[StrategyRepository, Depends(_strategy_repo_factory)]
 
 
 def _job_repo_factory(session: DbSession):