feat: add alert history

backend/app/models/alert.py

@@ -0,0 +1,33 @@
+from datetime import datetime
+
+from sqlalchemy import Boolean, Column, DateTime, Index, Integer, String, Text
+
+from app.core.database import Base
+
+
+class AlertHistory(Base):
+    """Persisted alert lifecycle record."""
+
+    __tablename__ = "alert_history"
+
+    id = Column(Integer, primary_key=True, index=True)
+    fingerprint = Column(String(64), unique=True, nullable=False, index=True)
+    rule = Column(String, nullable=False, index=True)
+    severity = Column(String, nullable=False, index=True)
+    domain = Column(String, nullable=True, index=True)
+    title = Column(String, nullable=False)
+    detail = Column(Text, nullable=False)
+    payload = Column(Text, nullable=True)
+    observed_count = Column(Integer, nullable=False, default=1)
+    is_active = Column(Boolean, nullable=False, default=True, index=True)
+    first_seen_at = Column(DateTime, default=datetime.utcnow, nullable=False, index=True)
+    last_seen_at = Column(DateTime, default=datetime.utcnow, nullable=False, index=True)
+    resolved_at = Column(DateTime, nullable=True, index=True)
+
+    __table_args__ = (
+        Index("ix_alert_history_active_last_seen", "is_active", "last_seen_at"),
+        Index("ix_alert_history_rule_domain", "rule", "domain"),
+    )
+
+    def __repr__(self):
+        return f"<AlertHistory {self.rule} active={self.is_active}>"