fix: use process.cwd() for public dir + simplified routes

- Changed publicDir to use process.cwd() for Vercel compatibility
- Simplified vercel.json routes: API -> server.js, everything else -> server.js
- Express.static will serve files from public/ directory

server.js

@@ -34,7 +34,7 @@ dotenv.config();
 const app = express();
 const PORT = process.env.PORT || 4444;
 const __filename = fileURLToPath(import.meta.url);
-const publicDir = path.join(dirname(__filename), "public");
+const publicDir = path.join(process.cwd(), "public");
 const allowedOrigins = process.env.ALLOWED_ORIGINS?.split(",");
 
 // ══════════════════════════════════════════════════════════════

vercel.json

@@ -13,7 +13,10 @@
       "headers": {
         "Access-Control-Allow-Origin": "*"
       }
+    },
+    {
+      "src": "/(.*)",
+      "dest": "server.js"
     }
-  ],
-  "outputDirectory": "public"
+  ]
 }