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/providers/Providers.tsx

@@ -0,0 +1,26 @@
+'use client';
+
+import { QueryClient, QueryClientProvider } from '@tanstack/react-query';
+import { Toaster } from 'sonner';
+import { useState } from 'react';
+
+export function Providers({ children }: { children: React.ReactNode }) {
+  const [queryClient] = useState(
+    () =>
+      new QueryClient({
+        defaultOptions: {
+          queries: {
+            staleTime: 60 * 1000, // 1 minute
+            refetchOnWindowFocus: false,
+          },
+        },
+      })
+  );
+
+  return (
+    <QueryClientProvider client={queryClient}>
+      {children}
+      <Toaster position="top-right" richColors />
+    </QueryClientProvider>
+  );
+}