Refactor: Simplify response message in upload endpoint to "OK"

server.js

@@ -195,11 +195,7 @@ function createApp(devMode = false) {
         `📁 Session created: ${sessionId.substring(0, 8)}... (${sessions.size}/${MAX_SESSIONS})`,
       );
 
-      res.json({
-        message: "Sample data uploaded successfully",
-        state: stateGuid,
-        sessionId: sessionId.substring(0, 8) + "...",
-      });
+      res.json({  message: "OK" });
     } catch (error) {
       console.error("⚠️ Upload endpoint exception occurred:", {
         message: error.message,