fix(security): enable Jinja2 autoescape to prevent XSS in gepa sample

CWE-79 (Cross-Site Scripting)

The gepa rater_lib.py instantiated jinja2.Environment() without autoescape=True,
allowing user_input and model_response to be rendered as raw HTML.

This fix:
- Enable autoescape=True in jinja2.Environment()
- Add explicit |e filters to {{user_input}} and {{model_response}} as defense-in-depth

Author: k4w1992-lgtm

contributing/samples/gepa/rater_lib.py

@@ -167,7 +167,7 @@ def __call__(self, messages: list[dict[str, Any]]) -> dict[str, Any]:
     Returns:
       A dictionary containing rating information including score.
     """
-    env = jinja2.Environment()
+    env = jinja2.Environment(autoescape=True)
     env.globals['user_input'] = (
         messages[0].get('parts', [{}])[0].get('text', '') if messages else ''
     )

contributing/samples/gepa/rubric_validation_template.txt

@@ -155,12 +155,12 @@ Verdict: no
   </available_tools>
 
   <main_prompt>
-  {{user_input}}
+  {{user_input|e}}
   </main_prompt>
 </user_prompt>
 
 <responses>
-{{model_response}}
+{{model_response|e}}
 </responses>
 
 <properties>