feat: add dark mode, fuzzy search, favorites, and URL sharing

Implemented Phases 5-7 of the implementation plan with major UX enhancements:

**Dark Mode (Phase 9)**
- Added ThemeToggle component with localStorage persistence
- System preference detection
- Smooth theme transitions
- Moon/Sun icon toggle in header

**Fuzzy Search with Fuse.js (Phase 5)**
- Integrated Fuse.js for intelligent font search
- 30% threshold for flexible matching
- Search by font name and filename
- Clear button for search input
- Much better than simple string matching

**Favorites & Recent Fonts System (Phase 7)**
- localStorage-based favorites with heart icon toggle
- Auto-tracking of recently used fonts (max 10)
- Filter tabs: All / Favorites / Recent
- Favorite hearts visible on hover
- Red filled heart for favorited fonts
- Stats showing favorite and recent counts

**Shareable URLs (Phase 6)**
- Encode text + font in URL parameters
- Auto-load from URL on page load
- Share button copies URL to clipboard
- Clean URL updates without page reload
- Perfect for sharing ASCII art creations

**Enhanced Font Selector**
- 3-tab filter system (All/Favorites/Recent)
- Visual feedback for selected fonts
- Empty states for each filter
- Font count statistics
- Heart icon for quick favoriting
- Recent fonts sorted by usage order

**UX Improvements**
- Copy feedback ("Copied to clipboard! ✓")
- Share feedback ("URL copied to clipboard! ✓")
- Responsive button layout
- Better empty states
- Improved accessibility with aria-labels

**Tech Highlights**
- Client-side localStorage management
- URL encoding/decoding utilities
- React hooks for state management
- Fuse.js fuzzy search integration
- Theme persistence across sessions

The app now has professional-grade features rivaling any modern web app!

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

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

components/layout/ThemeToggle.tsx

@@ -0,0 +1,42 @@
+'use client';
+
+import * as React from 'react';
+import { Moon, Sun } from 'lucide-react';
+import { Button } from '@/components/ui/Button';
+
+export function ThemeToggle() {
+  const [theme, setTheme] = React.useState<'light' | 'dark'>('light');
+
+  React.useEffect(() => {
+    // Check for saved theme preference or default to light
+    const savedTheme = localStorage.getItem('theme') as 'light' | 'dark' | null;
+    const prefersDark = window.matchMedia('(prefers-color-scheme: dark)').matches;
+    const initialTheme = savedTheme || (prefersDark ? 'dark' : 'light');
+
+    setTheme(initialTheme);
+    document.documentElement.classList.toggle('dark', initialTheme === 'dark');
+  }, []);
+
+  const toggleTheme = () => {
+    const newTheme = theme === 'light' ? 'dark' : 'light';
+    setTheme(newTheme);
+    localStorage.setItem('theme', newTheme);
+    document.documentElement.classList.toggle('dark', newTheme === 'dark');
+  };
+
+  return (
+    <Button
+      variant="outline"
+      size="icon"
+      onClick={toggleTheme}
+      aria-label="Toggle theme"
+      title={`Switch to ${theme === 'light' ? 'dark' : 'light'} mode`}
+    >
+      {theme === 'light' ? (
+        <Moon className="h-4 w-4" />
+      ) : (
+        <Sun className="h-4 w-4" />
+      )}
+    </Button>
+  );
+}