feat: initial Next.js 15 implementation with TypeScript and Tailwind CSS 4

Add complete project structure and foundation:

**Core Setup:**
- Next.js 15.5.6 with App Router and React 19
- TypeScript 5.7 with strict mode
- Tailwind CSS 4.1 with custom theme configuration
- ESLint and Prettier configuration

**Dependencies Installed:**
- @tanstack/react-query - Server state management
- zustand - Client state management
- framer-motion - Animations
- lucide-react - Icon library
- react-colorful - Color picker component
- cmdk - Command palette
- sonner - Toast notifications
- clsx + tailwind-merge - Class name utilities

**Project Structure:**
- app/ - Next.js App Router pages
- components/ - React components (ui, color, tools, layout, providers)
- lib/ - Utilities, API client, hooks, stores, constants
- tests/ - Unit and E2E test directories

**API Integration:**
- Type-safe Pastel API client with all 21 endpoints
- Complete TypeScript type definitions for requests/responses
- Error handling and response types

**UI Components:**
- Button component with variants (default, outline, ghost, destructive)
- Input component with focus states
- Providers wrapper (React Query, Toast)
- Root layout with Inter font and metadata

**Pages:**
- Home page with gradient hero and feature cards
- Links to playground and palette generation (pages pending)

**Configuration:**
- Tailwind with HSL color variables for theming
- Dark/light mode CSS variables
- Custom animations (fade-in, slide-up, slide-down)
- @tailwindcss/forms and @tailwindcss/typography plugins

Build successful: 102 kB First Load JS, static generation working.

Ready for color components and playground implementation.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

components/ui/input.tsx

@@ -0,0 +1,28 @@
+import * as React from 'react';
+import { cn } from '@/lib/utils/cn';
+
+export interface InputProps extends React.InputHTMLAttributes<HTMLInputElement> {}
+
+const Input = React.forwardRef<HTMLInputElement, InputProps>(
+  ({ className, type, ...props }, ref) => {
+    return (
+      <input
+        type={type}
+        className={cn(
+          'flex h-10 w-full rounded-md border border-input bg-background px-3 py-2',
+          'text-sm ring-offset-background file:border-0 file:bg-transparent',
+          'file:text-sm file:font-medium placeholder:text-muted-foreground',
+          'focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring',
+          'disabled:cursor-not-allowed disabled:opacity-50',
+          className
+        )}
+        ref={ref}
+        {...props}
+      />
+    );
+  }
+);
+
+Input.displayName = 'Input';
+
+export { Input };