feat: dark theme + toggle

[LEstradioto]

This PR is intended to start dark mode and toggle button (Nice addition with vanilla css!)

Changes

• light and dark CSS variables and updated hard-coded to use variables (tough to apply dark theme at flatpickr + tom select, it required lots of lines !!!)
• add toggle button on footer sidebar, toggle controller provides theme switching, system/theme persistence, smooth animate transition (is it too much?)
• changed precedence at _javascript.html to override flatpickr and tomselect
• changed margin and image size on nested fields

[excid3]

Thanks! Do you have any screenshots?

[LEstradioto]

👍

Video.sem.titulo.1.mp4