ci: add GitHub Actions workflow for PR validation

.github/workflows/ci.yml

@@ -0,0 +1,50 @@
+name: CI
+
+on:
+  pull_request:
+  push:
+    branches: [master]
+
+concurrency:
+  group: ci-${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+
+      - name: Install uv
+        run: python -m pip install --upgrade pip uv
+
+      - name: Cache uv
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cache/uv
+            backend/.venv
+          key: uv-${{ runner.os }}-${{ hashFiles('backend/uv.lock') }}
+
+      - name: Set up Node
+        uses: actions/setup-node@v4
+        with:
+          node-version: "20"
+          cache: npm
+          cache-dependency-path: frontend/package-lock.json
+
+      - name: Install dependencies
+        run: make setup
+
+      - name: Run checks
+        run: make check