fix: add concurrency control to prevent simultaneous deployments

- Added concurrency group 'deploy-vps' to all deployment workflows
- Prevents multiple deployments from running simultaneously on VPS
- Deployments now queue and run one at a time
- Fixes resource exhaustion when all apps deploy at once

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

.github/workflows/deploy-hackathon.yml

@@ -7,6 +7,10 @@ on:
     paths:
       - 'apps/hackathon/**' # Auto deploy when changes pushed to apps/hackathon
 
+concurrency:
+  group: deploy-vps
+  cancel-in-progress: false
+
 jobs:
   deploy:
     runs-on: ubuntu-latest