chore: add PR preview image build workflow

Author: github-copilot

.github/workflows/pr-preview-build.yml

@@ -0,0 +1,33 @@
+name: PR Preview Build
+
+on:
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  build-preview-image:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Python
+        uses: actions/setup-python@v4
+        with:
+          python-version: '3.10'
+      - name: Install test deps
+        run: python -m pip install --upgrade pip pytest
+      - name: Run tests
+        run: python -m pytest -q samples/book-app-project/tests
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v2
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v2
+      - name: Build Docker preview image
+        uses: docker/build-push-action@v4
+        with:
+          context: samples/book-app-project
+          file: samples/book-app-project/Dockerfile
+          load: true
+          push: false
+          tags: bookkeeper-app:pr-${{ github.event.pull_request.number }}