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/backend-deployment.yaml

@@ -44,7 +44,7 @@ spec:
       containers:
         - name: backend
           # Update with your registry and tag
-          image: gitea-http.taildb3494.ts.net/will/adopt-a-street/backend:latest
+          image: gitea-gitea-http.taildb3494.ts.net/will/adopt-a-street/backend:latest
           imagePullPolicy: Always
           ports:
             - containerPort: 5000