## Summary
* **What is the goal of this PR?**
Fix file browser failing to navigate into subdirectories with non-ASCII
(Korean/Unicode) folder names.
* **What changes are included?**
- Enable UTF-8 long file names in SdFat (`USE_UTF8_LONG_NAMES=1`)
- Add directory validation before iterating files
- Add `rewindDirectory()` call for stability
## Additional Context