refactor: simplify TOML common config handling by removing markers

- Remove COMMON_CONFIG_MARKER_START/END constants
- Simplify config snippet addition/removal logic
- Use natural append/replace approach instead of markers
- Fix unused variable warning
- Improve user experience with cleaner config output

src/utils/errorUtils.ts

@@ -35,4 +35,4 @@ export const extractErrorMessage = (error: unknown): string => {
   }
 
   return "";
-};
+};