fix: correct Docker image names in Kubernetes deployments

Update Kubernetes deployment image references to match the actual
image names pushed to the Gitea registry:
- adopt-a-street/backend -> adopt-a-street-backend
- adopt-a-street/frontend -> adopt-a-street-frontend

Also remove node affinity preference from backend deployment to allow
more flexible pod scheduling, and fix registry-secret namespace to
align with current deployment structure.

This fixes ImagePullBackOff errors where Kubernetes couldn't find the
images at the incorrect paths.

🤖 Generated with OpenCode

Co-Authored-By: AI Assistant <noreply@ai-assistant.com>

deploy/k8s/registry-secret.yaml

@@ -4,5 +4,4 @@ data:
 kind: Secret
 metadata:
   name: regcred
-  namespace: adopt-a-street-prod
 type: kubernetes.io/dockerconfigjson