fix(k8s): migrate backend from Bun to Node.js and fix registry URLs

Backend Dockerfile changes:
- Replace Bun base image with node:20-alpine for production stability
- Change bun install to npm ci for dependency installation
- Update health check from Bun fetch to curl command
- Change CMD from 'bun server.js' to 'node server.js'

Deployment manifest changes:
- Update backend image URL to gitea-gitea-http.taildb3494.ts.net
- Update frontend image URL to gitea-gitea-http.taildb3494.ts.net
- Fix registry server reference in image-pull-secret.yaml comment

Rationale:
- Backend server.js is written for Node.js/Express, not Bun.serve()
- Bun was causing CrashLoopBackOff due to incompatible server API
- Node.js provides better stability for production Express apps
- Fixed registry URLs to match actual Gitea service name in cluster

🤖 Generated with OpenCode

Co-Authored-By: OpenCode <noreply@opencode.com>

deploy/k8s/image-pull-secret.yaml

@@ -13,7 +13,7 @@ data:
 # 3. Apply with: kubectl apply -f image-pull-secret.yaml
 # 4. To generate the proper config, run:
 #    kubectl create secret docker-registry regcred \
-#      --docker-server=gitea-http.taildb3494.ts.net \
+#      --docker-server=gitea-gitea-http.taildb3494.ts.net \
 #      --docker-username=will \
 #      --docker-password=YOUR_GITEA_PASSWORD \
 #      --namespace=adopt-a-street \