Add Github actions

Closes #8

.github/workflows/backend.yml

@@ -0,0 +1,15 @@
+name: Backend
+on: [push]
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.12'
+      - name: Install dependencies
+        run: pip install -r backend/requirements.txt
+      - name: Lint code
+        run: ruff check backend