feat: implement core figlet converter with live preview

Implemented Phases 2-4 of the implementation plan:

**Phase 2: Font Management System**
- Created font loading service with caching
- Added API route to list all 373 figlet fonts
- Implemented font metadata types

**Phase 3: Core Figlet Engine**
- Built figlet.js wrapper service for ASCII art generation
- Added async/sync rendering methods
- Implemented debounced text updates (300ms)
- Created utility functions (cn, debounce)

**Phase 4: Main UI Components**
- Built reusable UI primitives (Button, Input, Card)
- Created TextInput component with character counter (100 char limit)
- Implemented FontPreview with loading states
- Added FontSelector with real-time search
- Built main FigletConverter orchestrating all components

**Features Implemented:**
- Live preview with 300ms debounce
- 373 fonts from xero/figlet-fonts collection
- Fuzzy font search
- Copy to clipboard
- Download as .txt file
- Responsive 3-column layout (mobile-friendly)
- Character counter
- Loading states
- Empty states

**Tech Stack:**
- Next.js 16 App Router with Turbopack
- React 19 with client components
- TypeScript with strict types
- Tailwind CSS 4 for styling
- figlet.js for rendering
- Font caching for performance

The application is fully functional and ready for testing!

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

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

components/ui/Card.tsx

@@ -0,0 +1,50 @@
+import * as React from 'react';
+import { cn } from '@/lib/utils/cn';
+
+const Card = React.forwardRef<HTMLDivElement, React.HTMLAttributes<HTMLDivElement>>(
+  ({ className, ...props }, ref) => (
+    <div
+      ref={ref}
+      className={cn('rounded-xl border bg-card text-card-foreground shadow', className)}
+      {...props}
+    />
+  )
+);
+Card.displayName = 'Card';
+
+const CardHeader = React.forwardRef<HTMLDivElement, React.HTMLAttributes<HTMLDivElement>>(
+  ({ className, ...props }, ref) => (
+    <div ref={ref} className={cn('flex flex-col space-y-1.5 p-6', className)} {...props} />
+  )
+);
+CardHeader.displayName = 'CardHeader';
+
+const CardTitle = React.forwardRef<HTMLDivElement, React.HTMLAttributes<HTMLDivElement>>(
+  ({ className, ...props }, ref) => (
+    <div ref={ref} className={cn('font-semibold leading-none tracking-tight', className)} {...props} />
+  )
+);
+CardTitle.displayName = 'CardTitle';
+
+const CardDescription = React.forwardRef<HTMLDivElement, React.HTMLAttributes<HTMLDivElement>>(
+  ({ className, ...props }, ref) => (
+    <div ref={ref} className={cn('text-sm text-muted-foreground', className)} {...props} />
+  )
+);
+CardDescription.displayName = 'CardDescription';
+
+const CardContent = React.forwardRef<HTMLDivElement, React.HTMLAttributes<HTMLDivElement>>(
+  ({ className, ...props }, ref) => (
+    <div ref={ref} className={cn('p-6 pt-0', className)} {...props} />
+  )
+);
+CardContent.displayName = 'CardContent';
+
+const CardFooter = React.forwardRef<HTMLDivElement, React.HTMLAttributes<HTMLDivElement>>(
+  ({ className, ...props }, ref) => (
+    <div ref={ref} className={cn('flex items-center p-6 pt-0', className)} {...props} />
+  )
+);
+CardFooter.displayName = 'CardFooter';
+
+export { Card, CardHeader, CardFooter, CardTitle, CardDescription, CardContent };