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/infrastructure/persistence/sqlalchemy/models/__init__.py

@@ -26,3 +26,7 @@ from app.infrastructure.persistence.sqlalchemy.models.selection import (  # noqa
     SelectionResultModel,
     SelectionSnapshotModel,
 )
+from app.infrastructure.persistence.sqlalchemy.models.signal import (  # noqa: F401
+    SignalEventModel,
+    SignalSnapshotModel,
+)

backend/app/infrastructure/persistence/sqlalchemy/models/signal.py

@@ -0,0 +1,41 @@
+"""交易信号表（M8.1）。
+
+signal_snapshot：一次信号运行的查询/规则/统计快照
+signal_event：逐信号（signal_type + score/price + trigger_reason JSON）
+"""
+
+from __future__ import annotations
+
+from datetime import date, datetime
+
+from sqlalchemy import BigInteger, Date, DateTime, Integer, Numeric, String, Text
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.infrastructure.persistence.sqlalchemy.base import Base
+
+PK_INT = BigInteger().with_variant(Integer, "sqlite")
+
+
+class SignalSnapshotModel(Base):
+    __tablename__ = "signal_snapshot"
+
+    id: Mapped[str] = mapped_column(String(32), primary_key=True)
+    as_of: Mapped[date] = mapped_column(Date, index=True)
+    query_json: Mapped[str] = mapped_column(Text)
+    rules_json: Mapped[str] = mapped_column(Text)
+    statistics_json: Mapped[str] = mapped_column(Text)
+    created_at: Mapped[datetime] = mapped_column(DateTime, index=True)
+
+
+class SignalEventModel(Base):
+    __tablename__ = "signal_event"
+
+    id: Mapped[int] = mapped_column(PK_INT, primary_key=True, autoincrement=True)
+    signal_id: Mapped[str] = mapped_column(String(32), index=True)
+    symbol: Mapped[str] = mapped_column(String(12))
+    signal_date: Mapped[date] = mapped_column(Date)
+    signal_type: Mapped[str] = mapped_column(String(8))
+    score: Mapped[float | None] = mapped_column(Numeric(14, 6), nullable=True)
+    price: Mapped[float | None] = mapped_column(Numeric(14, 4), nullable=True)
+    reason_json: Mapped[str | None] = mapped_column(Text, nullable=True)
+    created_at: Mapped[datetime] = mapped_column(DateTime)

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

@@ -0,0 +1,108 @@
+"""Signal Repository 的 SQLAlchemy 实现（M8.1）。"""
+
+from __future__ import annotations
+
+import json
+from datetime import date, datetime
+
+from sqlalchemy import select
+from sqlalchemy.orm import Session
+
+from app.domain.entities.signal import (
+    SignalEvent,
+    SignalMeta,
+    SignalResult,
+    SignalRules,
+    SignalStatistics,
+)
+from app.infrastructure.persistence.sqlalchemy.models.signal import (
+    SignalEventModel,
+    SignalSnapshotModel,
+)
+
+
+class SqlAlchemySignalRepository:
+    def __init__(self, session: Session) -> None:
+        self._session = session
+
+    def save(self, signal_id: str, result: SignalResult) -> None:
+        self._session.add(
+            SignalSnapshotModel(
+                id=signal_id,
+                as_of=result.as_of_date,
+                query_json=json.dumps(
+                    {
+                        "as_of": result.as_of_date.isoformat(),
+                        **{k: v for k, v in result.config_snapshot.items() if k != "as_of"},
+                    },
+                    ensure_ascii=False,
+                ),
+                rules_json=json.dumps(result.rules.model_dump(mode="json"), ensure_ascii=False),
+                statistics_json=json.dumps(result.statistics.model_dump(mode="json")),
+                created_at=datetime.now(),
+            )
+        )
+        now = datetime.now()
+        for e in result.events:
+            self._session.add(
+                SignalEventModel(
+                    signal_id=signal_id,
+                    symbol=e.symbol,
+                    signal_date=e.signal_date,
+                    signal_type=e.signal_type,
+                    score=e.score,
+                    price=e.price,
+                    reason_json=json.dumps(e.trigger_reason, ensure_ascii=False),
+                    created_at=now,
+                )
+            )
+        self._session.flush()
+
+    def get(self, signal_id: str) -> SignalResult | None:
+        snap = self._session.get(SignalSnapshotModel, signal_id)
+        if snap is None:
+            return None
+        rows = self._session.scalars(
+            select(SignalEventModel)
+            .where(SignalEventModel.signal_id == signal_id)
+            .order_by(SignalEventModel.signal_type, SignalEventModel.symbol)
+        ).all()
+        rules = SignalRules.model_validate_json(snap.rules_json)
+        stats = SignalStatistics.model_validate_json(snap.statistics_json)
+        return SignalResult(
+            as_of_date=snap.as_of,
+            rules=rules,
+            statistics=stats,
+            events=[
+                SignalEvent(
+                    symbol=r.symbol,
+                    signal_date=r.signal_date,
+                    signal_type=r.signal_type,
+                    score=float(r.score) if r.score is not None else None,
+                    price=float(r.price) if r.price is not None else None,
+                    trigger_reason=json.loads(r.reason_json or "[]"),
+                )
+                for r in rows
+            ],
+            config_snapshot={"as_of": snap.as_of.isoformat()},
+        )
+
+    def list_recent(self, as_of: date | None = None, limit: int = 20) -> list[SignalMeta]:
+        stmt = select(SignalSnapshotModel).order_by(SignalSnapshotModel.created_at.desc())
+        if as_of is not None:
+            stmt = stmt.where(SignalSnapshotModel.as_of == as_of)
+        stmt = stmt.limit(limit)
+        metas: list[SignalMeta] = []
+        for snap in self._session.scalars(stmt).all():
+            stats = SignalStatistics.model_validate_json(snap.statistics_json)
+            metas.append(
+                SignalMeta(
+                    id=snap.id,
+                    as_of=snap.as_of,
+                    buy=stats.buy,
+                    watch=stats.watch,
+                    sell=stats.sell,
+                    created_at=snap.created_at,
+                )
+            )
+        return metas