refactor server.js to support configurable data file path and ensure directory structure on startup

server.js

@@ -5,18 +5,22 @@ const { randomUUID } = require('crypto');
 
 const app = express();
 const PORT = process.env.PORT || 3000;
-const DATA_FILE = path.join(__dirname, 'data', 'results.json');
+// On HF Spaces the persistent bucket is mounted at /data; locally falls back to ./data/
+const DATA_FILE = process.env.DATA_PATH || path.join(__dirname, 'data', 'results.json');
 const IMAGES_DIR = path.join(__dirname, 'images');
 
 app.use(express.json());
 app.use(express.static(path.join(__dirname, 'public')));
 app.use('/images', express.static(IMAGES_DIR));
 
-// Auto-create required directories and data file on first run
-['data', 'images/real', 'images/fake'].forEach(dir => {
+// Ensure local image dirs exist (no-op when /data is an external mount)
+['images/real', 'images/fake'].forEach(dir => {
   const p = path.join(__dirname, dir);
   if (!fs.existsSync(p)) fs.mkdirSync(p, { recursive: true });
 });
+// Ensure the data file's parent directory exists, then seed an empty store
+const dataDir = path.dirname(DATA_FILE);
+if (!fs.existsSync(dataDir)) fs.mkdirSync(dataDir, { recursive: true });
 if (!fs.existsSync(DATA_FILE)) {
   fs.writeFileSync(DATA_FILE, JSON.stringify({ sessions: [], trials: [] }, null, 2));
 }