Add Gitea Actions workflow to build and push Docker images

Builds backend and frontend images and pushes them to the Gitea
Container Registry on every push to main.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.gitea/workflows/build.yml

@@ -0,0 +1,40 @@
+name: Build and Push Docker Images
+
+on:
+  push:
+    branches:
+      - main
+
+env:
+  REGISTRY: gitea.kzbikowski.pl
+
+jobs:
+  build-and-push:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Log in to Gitea Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ gitea.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build and push Backend
+        uses: docker/build-push-action@v5
+        with:
+          context: ./backend
+          push: true
+          tags: ${{ env.REGISTRY }}/${{ gitea.repository }}/backend:latest
+
+      - name: Build and push Frontend
+        uses: docker/build-push-action@v5
+        with:
+          context: ./frontend
+          push: true
+          tags: ${{ env.REGISTRY }}/${{ gitea.repository }}/frontend:latest