The output prefix was a plain text field; add a 'Browse…' button that opens a
file dialog to pick the output location. The chosen name is treated as a prefix
(the _process.h5 / .mtz / .cif suffixes are appended), so a trailing extension is
dropped, and the result is stored with native separators.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>