webui: edit box UX improvements

[abc-nix]

Warning: the code changes were generated with an LLM (breaking the AI Usage Policy of this project). I am making this clear so I don't get banned. As the AI would say, "the improvements are real", at least for me, but not up to the standards of this project. I hope they can inspire real human changes to improve my experience with OpenLumara.

This PR has three main parts:

1. Adds some improvements to the text-box used for editing (to not be a small minuscule text-box) by making it take the full width of the text bubble and expand the height to fit the text or a max 80% of the viewport height. I also repositions the view to the text box (as it would scroll away and I would have to scroll up to edit the text). The experience is much better for me when editing large blocks of text.
2. Fix an issue where, if a user reply contains an attachment, and I want to edit the message, I would get [object Object],[object Object] instead of the message. Now this is fixed (and I can edit the text) while preserving the attachment.
3. Manage attached files in Edit mode (can only remove files for now). I think a refactoring is needed to make it possible to add files in a more general way that works for both first message send and edit mode.

Note: if this kind of PR is not welcome, let me know (say explicitly) so I don't repeat the same mistake.

[Rose22]

oooh this is something ive been wanting to fix for a while but i had trouble figuring out how to do it! i'll test this pr and read the code to see if it's clean and clean it up if needed

[Rose22]

also, please remember to PR to the dev branch!

[abc-nix]

also, please remember to PR to the dev branch!

Sorry about that. I will make sure I do so in the future.