feat(signal): M8.1 交易信号引擎（规则 + signal_event 落库 + /api/signals）

- SignalRules（买入 rank 阈值/趋势 MA/动量 + 卖出区间/破位警示）+ SignalEvent
  （BUY/WATCH/SELL，score/price/trigger_reason 可解释）+ SignalResult/Meta
- quant/signal.generate_signals：与选股同一评分引擎取全市场 rank，按规则分类输出
- signal_snapshot/signal_event 表（migration d8e0b2f3c4d5，MySQL 已应用）+ Repo
- SignalService + POST /api/signals（同步+落库）、GET 详情/列表
- tests/test_signals.py（引擎分类/排序/破位不 BUY、service、API 提交读回）；全量 pytest 通过

backend/app/api/deps.py

@@ -11,6 +11,7 @@ from fastapi import Depends
 from sqlalchemy.orm import Session
 
 from app.application.services.selection_service import SelectionService
+from app.application.services.signal_service import SignalService
 from app.domain.repositories.composite import CompositeRepository
 from app.domain.repositories.factor import FactorRepository
 from app.domain.repositories.jobs import ExperimentRepository, JobRepository
@@ -20,6 +21,7 @@ from app.domain.repositories.market import (
     StockRepository,
 )
 from app.domain.repositories.selection import SelectionRepository
+from app.domain.repositories.signal import SignalRepository
 from app.infrastructure.persistence.sqlalchemy.repositories.composite_impl import (
     SqlAlchemyCompositeRepository,
 )
@@ -34,6 +36,9 @@ from app.infrastructure.persistence.sqlalchemy.repositories.market_impl import (
 from app.infrastructure.persistence.sqlalchemy.repositories.selection_impl import (
     SqlAlchemySelectionRepository,
 )
+from app.infrastructure.persistence.sqlalchemy.repositories.signal_impl import (
+    SqlAlchemySignalRepository,
+)
 from app.infrastructure.persistence.sqlalchemy.session import get_session
 from app.quant.engine import LocalEngine, QuantEngine
 from app.quant.service import ResearchService
@@ -65,6 +70,13 @@ def _service_factory(
     return ResearchService(stock_repo, daily_repo, engine)
 
 
+def _signal_service_factory(
+    stock_repo: Annotated[StockRepository, Depends(_stock_repo_factory)],
+    daily_repo: Annotated[DailyBarRepository, Depends(_daily_repo_factory)],
+) -> SignalService:
+    return SignalService(stock_repo, daily_repo)
+
+
 def _selection_service_factory(
     stock_repo: Annotated[StockRepository, Depends(_stock_repo_factory)],
     daily_repo: Annotated[DailyBarRepository, Depends(_daily_repo_factory)],
@@ -86,6 +98,10 @@ def _composite_repo_factory(session: DbSession) -> CompositeRepository:
     return SqlAlchemyCompositeRepository(session)
 
 
+def _signal_repo_factory(session: DbSession) -> SignalRepository:
+    return SqlAlchemySignalRepository(session)
+
+
 StockRepoDep = Annotated[StockRepository, Depends(_stock_repo_factory)]
 DailyRepoDep = Annotated[DailyBarRepository, Depends(_daily_repo_factory)]
 EngineDep = Annotated[QuantEngine, Depends(_engine_factory)]
@@ -94,6 +110,8 @@ SelectionServiceDep = Annotated[SelectionService, Depends(_selection_service_fac
 SelectionRepoDep = Annotated[SelectionRepository, Depends(_selection_repo_factory)]
 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)]
 
 
 def _job_repo_factory(session: DbSession):