DlgPrefLibrary: add reset-missing-tags checkbox to tab order

The new checkbox was missing from the dialog's explicit <tabstops>
order, so keyboard Tab navigation skipped it. Insert it between the
Serato and relative-path checkboxes to match its visual position.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: Gary

src/preferences/dialog/dlgpreflibrarydlg.ui

@@ -784,6 +784,7 @@
   <tabstop>checkBox_library_scan_summary</tabstop>
   <tabstop>checkBox_sync_track_metadata</tabstop>
   <tabstop>checkBox_serato_metadata_export</tabstop>
+  <tabstop>checkBox_reset_missing_tag_metadata</tabstop>
   <tabstop>checkBox_use_relative_path</tabstop>
   <tabstop>checkBox_edit_metadata_selected_clicked</tabstop>
   <tabstop>radioButton_dbclick_deck</tabstop>