k8s: wire RESEND_API_KEY env and drop to 1 replica

Registration emails were crashing the LiveView because RESEND_API_KEY
lived in aprs-secrets but was never injected into the container env,
so Resend.Swoosh.Adapter raised at delivery time after the user row
was already persisted.

k8s/deployment.yaml

@@ -4,7 +4,7 @@ metadata:
   name: aprs
   namespace: aprs
 spec:
-  replicas: 2
+  replicas: 1
   strategy:
     type: RollingUpdate
     rollingUpdate:
@@ -146,6 +146,11 @@ spec:
                 secretKeyRef:
                   name: aprs-secrets
                   key: SECRET_KEY_BASE
+            - name: RESEND_API_KEY
+              valueFrom:
+                secretKeyRef:
+                  name: aprs-secrets
+                  key: RESEND_API_KEY
           envFrom:
             - secretRef:
                 name: aprs-db