Fix prompt templates loading and structure

app.py

@@ -69,7 +69,8 @@ model = OpenAIModel(
 image_generation_tool = load_tool("agents-course/text-to-image", trust_remote_code=True)
 
 with open("prompts.yaml", 'r') as stream:
-    prompt_templates = yaml.safe_load(stream)
+    yaml_content = yaml.safe_load(stream)
+    prompt_templates = yaml_content['prompt_templates']  # Extract the prompt_templates section
     
 agent = CodeAgent(
     model=model,