fix: configure kubectl with kubeconfig secret in CI

Add kubeconfig secret mounting for deploy step to authenticate
with Kubernetes cluster.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

.woodpecker.yml

@@ -25,7 +25,10 @@ steps:
 
   deploy:
     image: bitnami/kubectl:latest
+    secrets: [kubeconfig]
     commands:
+      - mkdir -p ~/.kube
+      - echo "$KUBECONFIG" > ~/.kube/config
       - kubectl set image deployment/research-notes web=registry.threesix.ai/research-notes/web:${CI_COMMIT_SHA:0:8} -n projects
       - kubectl rollout status deployment/research-notes -n projects --timeout=120s
     when: