Add concurrency control to deploy workflow

- Cancels any in-progress deployment when a new commit is pushed
- Prevents multiple deployments from running simultaneously
- Uses concurrency group based on branch ref
- Saves CI/CD resources and prevents conflicting deployments

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

.github/workflows/deploy.yml

@@ -4,6 +4,11 @@ on:
   push:
     branches: [main]
 
+# Cancel in-progress runs when a new run is triggered
+concurrency:
+  group: deploy-${{ github.ref }}
+  cancel-in-progress: true
+
 env:
   REGISTRY: ghcr.io
   IMAGE_NAME: ${{ github.repository }}