Issue #3521351: Fix provider/model refresh and multivalue remove button

Closes #3521351

This MR:

• Updates the Provider AJAX callback so the Model & Voice dropdowns truly rebuild.
• Restores the standard Drupal “Remove” button on multivalue fields and hides weight controls.
• Ensures the selected provider and model stick through form rebuilds.
• Cleans up stray .DS_Store files.

Ready for review and testing—thanks!