Upgrade: Tailwind v4 (#5246)

* temp: move tailwind calls out of the layer

* temp: ts tailwind config

* upgrade: Tailwind v4
This got a little out of hand.
Had to add a relative reference to the stylesheet in any component that uses @apply instead of the utility classes directly.

* upgrade: bg-opacity is now a modifier

* fix: Classic menu buttons assume a border

* Update test expectations [skip ci]

* fix: New preflight removal pattern

* fix: Skeletons don't have skin

* Update test expectations [skip ci]

* fix: Missing @reference

* [auto-fix] Apply ESLint and Prettier fixes

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src/components/sidebar/tabs/NodeLibrarySidebarTab.vue

@@ -3,7 +3,7 @@
     <SidebarTabTemplate
       v-if="!isHelpOpen"
       :title="$t('sideToolbar.nodeLibrary')"
-      class="bg-[var(--p-tree-background)]"
+      class="bg-(--p-tree-background)"
     >
       <template #tool-buttons>
         <Button