Improve JsonParseError message formatting

Use heredoc for better readability of multi-line error message.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: justin808

lib/react_on_rails/json_parse_error.rb

@@ -7,7 +7,11 @@ class JsonParseError < ::ReactOnRails::Error
     def initialize(parse_error:, json:)
       @json = json
       @original_error = parse_error
-      message = "#{parse_error.message}\n\n#{Utils.default_troubleshooting_section}"
+      message = <<~MSG
+        #{parse_error.message}
+
+        #{Utils.default_troubleshooting_section}
+      MSG
       super(message)
     end