fix ppm bug

drb-c2-core/app/routers/nodes.py

@@ -1,4 +1,5 @@
 import secrets
+from typing import Optional
 from fastapi import APIRouter, HTTPException, Depends, Query
 from app.models import CommandPayload
 from app.internal import firestore as fstore
@@ -97,7 +98,7 @@ async def assign_system(
     node_id: str,
     system_id: str,
     hardware_preset: str = Query("rtl-sdr-v3"),
-    ppm_override: float = Query(None),
+    ppm_override: Optional[float] = Query(None),
 ):
     """
     Assign a system to a node. Fetches the system config from Firestore