Add GHCR upload action

.github/workflows/docker.yml

@@ -0,0 +1,33 @@
+name: Build & Push Docker image to GHCR
+
+on:
+    push:
+        branches: [main] # or your default branch
+    workflow_dispatch: # allow manual trigger
+
+permissions:
+    contents: read
+    packages: write # needed to push to GHCR
+
+jobs:
+    build-and-push:
+        runs-on: ubuntu-latest
+
+        steps:
+            - name: Checkout code
+              uses: actions/checkout@v4
+
+            - name: Log in to GHCR
+              uses: docker/login-action@v3
+              with:
+                  registry: ghcr.io
+                  username: ${{ github.actor }}
+                  password: ${{ secrets.GITHUB_TOKEN }}
+
+            - name: Build Docker image
+              run: |
+                  docker build -t ghcr.io/${{ github.repository_owner }}/class-compass-server-mini:latest .
+
+            - name: Push image to GHCR
+              run: |
+                  docker push ghcr.io/${{ github.repository_owner }}/class-compass-server-mini:latest