fix: Fix ShadCN UI styles in Nx monorepo with Tailwind v4

[naaa760]

#7828

Problem
ShadCN UI components were rendering without styles in our Nx monorepo setup with Tailwind CSS v4 and Next.js 15. The issue was caused by incorrect Tailwind content paths and missing shared UI library structure.

Solution

• Fixed Tailwind config to properly scan all monorepo directories (apps/, packages/, components/, etc.)
• Created shared UI package** (packages/ui/) with proper TypeScript configuration and build setup
• Updated PostCSS config to work correctly with monorepo structure
• Added workspace dependency and TypeScript path mapping for the UI package
• Created test page to demonstrate working components with proper styling

Changes

• tailwind.config.cjs - Updated content paths for monorepo
• apps/v4/postcss.config.mjs - Added config path reference
• apps/v4/package.json - Added @workspace/ui dependency
• apps/v4/tsconfig.json - Added workspace path mapping
• packages/ui/ - New shared UI package with Button component
• apps/v4/app/test-ui/page.tsx - Test page showing working components

Testing

Visit /test-ui to see all button variants, sizes, and states working with proper Tailwind v4 styling.

This resolves the issue where ShadCN UI components were unstyled in the monorepo setup.

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