RM-217: Add per-panel customization for multi-panel creation

[biast12]

Description

RM-217
Implements support for custom labels, descriptions, and emojis (both unicode and custom) for each panel in multi-panel creation and editing. Updates backend API endpoints and message rendering logic to handle these customizations, and enhances the frontend form to allow users to configure these options per panel, including validation and improved UX for dropdown mode.

This PR needs this database PR to be accepted first: TicketsBot-cloud/database#15

Type of Change

• Bug fix
• New feature
• Breaking change

Testing

make at least 2 panels, 1 of them needs to only use an emoji (no button text/label), make a multipanel and add those two panels to it, add a new label or emoji and save, when that works, then change the multipanel to be a dropdown, now you need to have a label, and you can add a description

Checklist

• My code follows the style of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works