fix: clean up empty file after failed wl-paste clipboard extraction

When wl-paste produces empty output, the destination file was left as
a 0-byte orphan. Added dest.unlink() before returning False, matching
the existing cleanup pattern in the exception handler.

Authored by 0xbyt4.

Co-authored-by: 0xbyt4 <0xbyt4@users.noreply.github.com>

hermes_cli/clipboard.py

@@ -254,6 +254,7 @@ def _wayland_save(dest: Path) -> bool:
             )
 
         if not dest.exists() or dest.stat().st_size == 0:
+            dest.unlink(missing_ok=True)
             return False
 
         # BMP needs conversion to PNG (common in WSLg where only BMP