Update gradio-server.mdx

I believe the HF gradio spaces requires naming the gradio application to app.py.

Author: csabakecskemeti

units/en/unit2/gradio-server.mdx

@@ -165,8 +165,9 @@ textblob
 
 3. Push your code to the Space:
 ```bash
+cp server.py app.py
 git init
-git add server.py requirements.txt
+git add app.py requirements.txt
 git commit -m "Initial commit"
 git remote add origin https://huggingface.co/spaces/YOUR_USERNAME/mcp-sentiment
 git push -u origin main
@@ -185,4 +186,4 @@ Now that we have our MCP server running, we'll create clients to interact with i
 2. Implement a SmolAgents-based Python client
 3. Test both clients with our deployed server
 
-Let's move on to building our first client! 
+Let's move on to building our first client!