Setting manually morph ID does not create morph animation between slides #54

Hi, great project, love it. Thanks for your work!

What happened
Setting Same morph ID on two elements does not trigger morph animation between slides. This is quite terrible if you want to edit element back and forth between slides, it makes adding elements with clean animations

bug_morph_id.html

on previous slides impossible.

The morph animation using ID doesn't work without duplicating the previous slide.
Setting the morph ID of a previous element directly set the pairing key (impossible to clear) and no morph animation.

Steps to reproduce

1. Create an element
2. Copy the element to the next slide + set the same morph ID
3. set both slide on Morph Transition
4. play Slideshow

Environment

• App version (About dialog, or the shell's APP_VERSION): v1.0.8
• Browser + version: Brave
• OS: MacOS 26.5.2 (25F84)