[WIP] Upgrade to Tailwind v4

[ylynfatt]

This is still a WIP, but I began working on the changes.

It seems for now Filament have pinned v3 of their package to v3 of Tailwind. See recent pull request by the Filament team. As such, I had to make a few adjustments to how the filament CSS was imported (some not seen in this pull request). So for example, some modifications were made to vendor/filament/filament/resources/css/theme.css and vendor/filament/filament/resources/css/index.css in order for the dashboard/theme.css in Cachet core to compile properly.