feat: add icons to buttons and auto-refresh on stop, implement GitHub Actions CI/CD

UI Enhancements:
- Add Font Awesome icons to all control buttons (stop, start, restart, manage volumes)
- Auto-refresh page after server stop with smooth UI transitions
- Hide/show appropriate buttons based on server state (Restart vs Manage Volumes)
- Re-inject icons removed by JupyterHub's DOM manipulation

Technical Implementation:
- MutationObserver watches for JupyterHub DOM changes after stop
- Immediate UI state correction before page refresh
- Comprehensive console logging for debugging

CI/CD:
- Add GitHub Actions workflow for Dockerfile validation with hadolint
- Triggers on push to main, version tags, and pull requests
- Uses hadolint to ensure Dockerfile best practices

.github/workflows/docker-build.yml

@@ -0,0 +1,29 @@
+name: Validate Dockerfile
+
+on:
+  push:
+    branches:
+      - main
+    tags:
+      - '*_cuda-*_jh-*'
+  pull_request:
+    branches:
+      - main
+  workflow_dispatch:
+
+jobs:
+  validate:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Lint Dockerfile with hadolint
+        uses: hadolint/hadolint-action@v3.1.0
+        with:
+          dockerfile: services/jupyterhub/Dockerfile.jupyterhub
+          ignore: DL3008,DL3013,DL3015,DL3059,DL3027,DL4006,SC2006,SC1008,DL3046,SC2153,DL3001,SC2016,SC2002
+
+      - name: Validation completed
+        run: echo "Dockerfile validation completed successfully"