Add alert management functionality in backend and frontend

This commit introduces alert management capabilities, including creating, updating, listing, and removing custom SQL-based alerts in the backend. It adds the necessary database migrations, API endpoints, and frontend pages to manage alerts, enabling users to define thresholds and monitor system health effectively.

backend/app/models/models.py

@@ -1,5 +1,5 @@
 from datetime import datetime
-from sqlalchemy import JSON, DateTime, Float, ForeignKey, Integer, String, Text, func
+from sqlalchemy import JSON, Boolean, DateTime, Float, ForeignKey, Integer, String, Text, func
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 from app.core.db import Base
 
@@ -32,6 +32,7 @@ class Target(Base):
 
     metrics: Mapped[list["Metric"]] = relationship(back_populates="target", cascade="all, delete-orphan")
     query_stats: Mapped[list["QueryStat"]] = relationship(back_populates="target", cascade="all, delete-orphan")
+    alert_definitions: Mapped[list["AlertDefinition"]] = relationship(back_populates="target", cascade="all, delete-orphan")
 
 
 class Metric(Base):
@@ -73,3 +74,27 @@ class AuditLog(Base):
     payload: Mapped[dict] = mapped_column(JSON, nullable=False, default=dict)
 
     user: Mapped[User | None] = relationship(back_populates="audit_logs")
+
+
+class AlertDefinition(Base):
+    __tablename__ = "alert_definitions"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True)
+    name: Mapped[str] = mapped_column(String(160), nullable=False)
+    description: Mapped[str | None] = mapped_column(Text, nullable=True)
+    target_id: Mapped[int | None] = mapped_column(ForeignKey("targets.id", ondelete="CASCADE"), nullable=True, index=True)
+    sql_text: Mapped[str] = mapped_column(Text, nullable=False)
+    comparison: Mapped[str] = mapped_column(String(10), nullable=False, default="gte")
+    warning_threshold: Mapped[float | None] = mapped_column(Float, nullable=True)
+    alert_threshold: Mapped[float] = mapped_column(Float, nullable=False)
+    enabled: Mapped[bool] = mapped_column(Boolean, nullable=False, default=True)
+    created_by_user_id: Mapped[int | None] = mapped_column(ForeignKey("users.id"), nullable=True, index=True)
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), nullable=False, server_default=func.now(), index=True)
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True),
+        nullable=False,
+        server_default=func.now(),
+        onupdate=func.now(),
+    )
+
+    target: Mapped[Target | None] = relationship(back_populates="alert_definitions")