feat: add WonderQ admin backend

Add FastAPI admin/public API service, database setup, Docker deployment files, docs, and tests.

tests/test_app.py

@@ -0,0 +1,9 @@
+from fastapi.testclient import TestClient
+from app.main import create_app
+
+
+def test_health_endpoint():
+    client = TestClient(create_app())
+    response = client.get("/health")
+    assert response.status_code == 200
+    assert response.json() == {"ok": True, "service": "miniapp-api"}