```

Switch to timezone.utc for event date validation

Replaced ZoneInfo('UTC') with timezone.utc in event date validation to ensure consistency and compatibility with standard libraries. Simplifies datetime handling and avoids potential issues with external dependencies.
```

backend/app/schemas/events.py

@@ -1,4 +1,4 @@
-from datetime import datetime, time
+from datetime import datetime, time, timezone
 from typing import Dict, Optional, List, Union
 from uuid import UUID
 from pydantic import BaseModel, Field, field_validator
@@ -39,7 +39,7 @@ class EventBase(BaseModel):
 
     @field_validator('event_date')
     def validate_event_date(cls, v):
-        if v < datetime.now(ZoneInfo('UTC')):
+        if v < datetime.now(tz=timezone.utc):
             raise ValueError("Event date cannot be in the past")
         return v