feat: Update shadcn to use latest shadcn components and Tailwind v4 (#4720)

* feat: bump shadcn to v4 components

* feat: update tailwindcss to v4.1.11 and add @tailwindcss/cli for compiling css. also remove unnecessary postcss

* feat: switch to @tailwindcss/cli for CSS build process

* feat: update IconButton to use class-variance-authority for variant props

* feat: add new CSS themes for styling with Tailwind CSS v4

* feat: update stylesheet paths to use v4 versions for shadcn themes

* feat: update Jest snapshots for TextAreaWidget and CheckboxesWidget with new class names and attributes

* feat: update SubmitButton layout to use flexbox for better alignment and RTL support

* Revert "feat: update SubmitButton layout to use flexbox for better alignment and RTL support"

This reverts commit b0a3f28.

* feat: update CHANGELOG for version 6.0.0-beta.15 with component bumps and theme updates

* chore: remove unnecessary components.json

* Update CHANGELOG.md

---------

Co-authored-by: Heath C <51679588+heath-freenome@users.noreply.github.com>

Author: tuanphung2308

CHANGELOG.md

@@ -50,6 +50,13 @@ should change the heading of the (upcoming) version to include a major version b
 
 - Fixed checkbox widget to use current value instead of event target in onFocus/onBlur handlers, fixing [#4704](https://github.com/rjsf-team/react-jsonschema-form/issues/4704)
 
+## @rjsf/shadcn
+
+- Bump `@shadcn/ui` components to use latest version from https://ui.shadcn.com/
+- Bump `tailwindcss` to using v4 and css compiling process to use latest `@tailwindcss/cli`
+- Remove `postcss` due to new Oxide compiler of tailwindcss
+- Update playground themes with `default`, `Amethyst Haze`, `Caffeine`, `Claude`, `Neo Brutalism`, `Pastel Dreams`, `Soft Pop`, `Twitter`, `Vercel`
+
 ## @rjsf/utils
 
 - Updated `UiSchema` type to support dynamic array item UI schemas - the `items` property can now be either a `UiSchema` object or a function that returns a `UiSchema` ([#4706](https://github.com/rjsf-team/react-jsonschema-form/pull/4706))