feat: add app factory with health endpoint and test infrastructure

tests/test_app.py

@@ -0,0 +1,15 @@
+from httpx import AsyncClient
+
+
+async def test_health_endpoint(client: AsyncClient) -> None:
+    response = await client.get("/health")
+    assert response.status_code == 200
+    data = response.json()
+    assert data["status"] == "ok"
+
+
+async def test_app_has_title(client: AsyncClient) -> None:
+    response = await client.get("/openapi.json")
+    assert response.status_code == 200
+    data = response.json()
+    assert data["info"]["title"] == "FastAPI OIDC OP"