docs: correct Ollama model references to gemma4:e2b

The deployed agent model is gemma4:e2b; these references still named
mistral-nemo, so the setup and troubleshooting steps checked for a model
that is no longer expected to be present.

Co-Authored-By: Claude <noreply@anthropic.com>

AGENTS.md

@@ -270,7 +270,7 @@ echo $WEBBER_API_URL  # Should be http://localhost:8095
 curl http://192.168.86.149:11434/api/tags
 
 # Check model is available
-curl http://192.168.86.149:11434/api/tags | grep mistral-nemo
+curl http://192.168.86.149:11434/api/tags | grep gemma4
 ```
 
 ### Tests failing