docs: Add .env.example with debug mode documentation

.env.example

@@ -0,0 +1,5 @@
+# Debug Mode
+# Set to 'true' to enable debug mode which shows LLM prompts and responses
+# This is useful for debugging AI behavior
+NEXT_PUBLIC_DEBUG=false
+

.gitignore

@@ -32,6 +32,7 @@ yarn-error.log*
 
 # env files (can opt-in for committing if needed)
 .env*
+!.env.example
 
 # vercel
 .vercel