**ci(workflows): update permissions and token usage for deploy workflow**

### Changes:
- **deploy-demo.yml**:
  - Added `contents: write` permissions to ensure the workflow can access repository content during operations.
  - Used `${{ secrets.GITHUB_TOKEN }}` for authentication in the deployment step.

- **package.json**:
  - Removed the `deploy:demo` script and its `gh-pages` dependency to clean up unused scripts and dependencies.

### Purpose:
Enhanced the deploy workflow by explicitly defining required permissions and securely managing authentication. Simplified the configuration by removing outdated scripts and dependencies.

.github/workflows/deploy-demo.yml

@@ -8,6 +8,8 @@ on:
 jobs:
   build-and-deploy:
     runs-on: ubuntu-latest
+    permissions:
+      contents: write
     steps:
       - name: Checkout 🛎️
         uses: actions/checkout@v3
@@ -31,3 +33,4 @@ jobs:
         with:
           folder: examples
           branch: gh-pages
+          token: ${{ secrets.GITHUB_TOKEN }}