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

Author: tuanphung2308

CHANGELOG.md

@@ -15,6 +15,15 @@ it according to semantic versioning. For example, if your PR adds a breaking cha
 should change the heading of the (upcoming) version to include a major version bump.
 
 -->
+# 6.0.0-beta.15
+
+## @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`
+
 # 6.0.0-beta.14
 
 ## @rjsf/core