admin-ui: prefill the selected preset name when saving #78

Summary

When a preset is selected in Custom Client Builder, using Save preset should automatically fill the preset name with the currently selected preset’s name.

Expected behavior

• Selecting an existing preset and choosing Save preset pre-populates the name field with that preset’s current name.
• The user can still edit the name before saving if the UI supports renaming/copying presets.

Context

This avoids re-entering a name when saving changes to the selected preset.