feat: fix TypeScript declarations generation with tsup

[christoph2806]

Fix TypeScript Declarations Generation with tsup

🎯 Resolves Issue #41

This PR completely resolves the missing TypeScript declaration files issue by replacing the complex manual build setup with tsup, a specialized TypeScript library bundler.

🔧 Changes Made

Build System Overhaul

• Replaced complex vite build && tsc --project tsconfig.build.json with simple tsup
• Added tsup.config.ts with proper React component support
• Removed manual TypeScript configuration files (tsconfig.build.json, vite.css.config.ts)
• Updated package.json exports to match new file structure

Key Improvements

• ✅ Automatic TypeScript declarations generation (index.d.ts, index.d.cts)
• ✅ Proper React component support with JSX handling
• ✅ Multiple output formats (ESM + CommonJS)
• ✅ CSS bundling with source maps maintained
• ✅ Browser compatibility with crypto polyfills
• ✅ Simplified build process - single command

Technical Details

• Platform: browser for proper Web API handling
• External dependencies: React, React-DOM (peer dependencies)
• Bundle nanoid: Ensures browser-compatible crypto usage
• Target: ES2020 for modern browser support

🧪 Testing

• ✅ Build verification: All outputs generated correctly
• ✅ TypeScript compilation: Declarations work with consuming apps
• ✅ Component exports: All 64+ components properly exported
• ✅ Browser compatibility: No Node.js crypto imports in bundle
• ✅ Showcase build: Consuming application builds successfully
• ✅ All tests pass: Unit tests, accessibility tests, linting

📦 Generated Files

dist/
├── index.js          # ESM bundle
├── index.cjs         # CommonJS bundle
├── index.d.ts        # TypeScript declarations
├── index.d.cts       # CommonJS TypeScript declarations
├── index.css         # Styles
└── *.map             # Source maps

🚀 Impact

• Developers can now import components with full TypeScript support
• Build process is significantly simplified and more reliable
• Package quality improved with proper library tooling
• Future maintenance easier with specialized build tool

📋 Checklist

• TypeScript declarations generated correctly
• All components exported with proper types
• Browser compatibility maintained
• Build process simplified
• Tests passing
• Documentation updated (if needed)

This change resolves the core issue and provides a robust foundation for TypeScript support in the ui-kit package.