Svelte5 migrate dispatch

[AmandaSternberg-creator]

Hi, I started exploring this, but I don’t expect so much of it since Daimen hasn’t given the go-ahead and some related PRs (#4029, #4289) might need to be merged first.

However, I set up a proposal for how we could adadress the deprecated createEventDispatcher usage in Svelte components (#4408). In this PR I refactored one component (TagAddButton.svelte) to use a callback prop (onTagAppend) instead of dispatching "tagappend" events and updated the parent accordingly.

This PR is intended as a starting point only. Any thoughts or suggestions are highly appreciated before I continue! Thanks :)