Add Forgejo CI workflow to build and push Docker image

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.forgejo/workflows/docker.yaml

@@ -0,0 +1,19 @@
+on:
+  push:
+    branches:
+      - main
+
+jobs:
+  build:
+    runs-on: docker
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Build and push Docker image
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          push: true
+          tags: ${{ gitea.server_url }}/${{ gitea.repository }}:latest
+          username: ${{ gitea.actor }}
+          password: ${{ secrets.FORGEJO_TOKEN }}