fix: escape curly braces in reflection prompt for LangChain

The JSON examples in REFLECT_ON_ROADMAP_SYSTEM_PROMPT were being
interpreted as template variables by LangChain's ChatPromptTemplate.
Double curly braces escape them as literal text.

Author: jwm4

review_roadmap/agent/prompts.py

@@ -62,12 +62,12 @@
 ## Response Format
 If the roadmap passes review, respond with EXACTLY this JSON:
 ```json
-{"passed": true, "notes": "Self-review: [brief note on quality]"}
+{{"passed": true, "notes": "Self-review: [brief note on quality]"}}
 ```
 
 If issues need fixing, respond with EXACTLY this JSON:
 ```json
-{"passed": false, "feedback": "[specific issues to fix, be concise]"}
+{{"passed": false, "feedback": "[specific issues to fix, be concise]"}}
 ```
 
 Be rigorous but not pedantic. Only fail roadmaps with genuine issues that would confuse or mislead a reviewer.