fix(deploy): use maxSurge=0 for rolling update to fit resource quota

maxSurge=1 requires a second pod during rollout, but the tenant
ResourceQuota (1 CPU limit) is already at 900m — the extra 250m
exceeds the cap and the pod can't schedule, causing a 5min timeout.

Switch to maxSurge=0/maxUnavailable=1 (kill-then-start) to stay
within quota. Matches the web deployment strategy.

backend/deploy/helm/templates/deployment.yaml

@@ -12,8 +12,8 @@ spec:
   strategy:
     type: RollingUpdate
     rollingUpdate:
-      maxUnavailable: 0
-      maxSurge: 1
+      maxSurge: 0
+      maxUnavailable: 1
   selector:
     matchLabels:
       {{- include "marktvogt-backend.selectorLabels" . | nindent 6 }}