fix: Add Docker login and permissions to CI workflow

This commit fixes the Docker image push failure in the CI workflow
by adding the necessary Docker login step and ensuring the correct
permissions are set for the GITHUB_TOKEN.

- Added a Docker login step using `docker/login-action@v3` to the
  `Build Docker Image` job in `.github/workflows/ci.yaml`. This
  authenticates to GHCR before attempting to push images.
- Added a `permissions` block to the `Build Docker Image` job, granting
  `packages: write` scope to the `GITHUB_TOKEN`. This is required
  to allow pushing packages to the GitHub Container Registry.

.github/workflows/ci.yaml

@@ -27,6 +27,9 @@ jobs:
   build:
     name: Build Docker Image
     runs-on: ubuntu-latest
+    permissions:
+      contents: read # Needed to checkout the repository
+      packages: write # Needed to push Docker images to GHCR
     steps:
       - name: Check out code
         uses: actions/checkout@v3
@@ -50,6 +53,13 @@ jobs:
             # Tag with 'latest' if on the main branch (though this workflow only runs on PRs to main)
             type=ref,event=branch,pattern=main,value=latest
 
+      - name: Log in to GitHub Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
       - name: Build Docker image
         uses: docker/build-push-action@v4
         with: