chore: scaffold backend venv, health check, systemd unit

backend/tests/test_health.py

@@ -0,0 +1,10 @@
+from fastapi.testclient import TestClient
+
+from app.main import app
+
+
+def test_healthz_returns_ok():
+    client = TestClient(app)
+    response = client.get("/healthz")
+    assert response.status_code == 200
+    assert response.json() == {"status": "ok"}