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/schemas/alert.py

@@ -0,0 +1,74 @@
+from datetime import datetime
+from pydantic import BaseModel, Field
+
+
+class AlertDefinitionBase(BaseModel):
+    name: str = Field(min_length=2, max_length=160)
+    description: str | None = None
+    target_id: int | None = None
+    sql_text: str = Field(min_length=8, max_length=4000)
+    comparison: str = "gte"
+    warning_threshold: float | None = None
+    alert_threshold: float
+    enabled: bool = True
+
+
+class AlertDefinitionCreate(AlertDefinitionBase):
+    pass
+
+
+class AlertDefinitionUpdate(BaseModel):
+    name: str | None = Field(default=None, min_length=2, max_length=160)
+    description: str | None = None
+    target_id: int | None = None
+    sql_text: str | None = Field(default=None, min_length=8, max_length=4000)
+    comparison: str | None = None
+    warning_threshold: float | None = None
+    alert_threshold: float | None = None
+    enabled: bool | None = None
+
+
+class AlertDefinitionOut(AlertDefinitionBase):
+    id: int
+    created_by_user_id: int | None = None
+    created_at: datetime
+    updated_at: datetime
+
+    model_config = {"from_attributes": True}
+
+
+class AlertDefinitionTestRequest(BaseModel):
+    target_id: int
+    sql_text: str = Field(min_length=8, max_length=4000)
+
+
+class AlertDefinitionTestResponse(BaseModel):
+    ok: bool
+    value: float | None = None
+    error: str | None = None
+
+
+class AlertStatusItem(BaseModel):
+    alert_key: str
+    source: str
+    severity: str
+    category: str
+    name: str
+    description: str
+    target_id: int
+    target_name: str
+    value: float | None = None
+    warning_threshold: float | None = None
+    alert_threshold: float | None = None
+    comparison: str = "gte"
+    message: str
+    checked_at: datetime
+    sql_text: str | None = None
+
+
+class AlertStatusResponse(BaseModel):
+    generated_at: datetime
+    warnings: list[AlertStatusItem]
+    alerts: list[AlertStatusItem]
+    warning_count: int
+    alert_count: int