feat: add monitoring trends

backend/app/monitoring/exceptions.py

@@ -0,0 +1,13 @@
+"""Monitoring domain exceptions."""
+
+
+class MonitoringError(Exception):
+    """Base monitoring-domain error."""
+
+
+class MonitoringValidationError(MonitoringError):
+    """The requested trend scope or range is invalid."""
+
+
+class MonitoringScopeNotFound(MonitoringError):
+    """The requested durable scope does not exist."""