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>

lib/storage/favorites.ts

@@ -0,0 +1,70 @@
+'use client';
+
+const FAVORITES_KEY = 'figlet-ui-favorites';
+const RECENT_FONTS_KEY = 'figlet-ui-recent-fonts';
+const MAX_RECENT = 10;
+
+export function getFavorites(): string[] {
+  if (typeof window === 'undefined') return [];
+
+  try {
+    const stored = localStorage.getItem(FAVORITES_KEY);
+    return stored ? JSON.parse(stored) : [];
+  } catch {
+    return [];
+  }
+}
+
+export function addFavorite(fontName: string): void {
+  const favorites = getFavorites();
+  if (!favorites.includes(fontName)) {
+    favorites.push(fontName);
+    localStorage.setItem(FAVORITES_KEY, JSON.stringify(favorites));
+  }
+}
+
+export function removeFavorite(fontName: string): void {
+  const favorites = getFavorites();
+  const filtered = favorites.filter(f => f !== fontName);
+  localStorage.setItem(FAVORITES_KEY, JSON.stringify(filtered));
+}
+
+export function isFavorite(fontName: string): boolean {
+  return getFavorites().includes(fontName);
+}
+
+export function toggleFavorite(fontName: string): boolean {
+  const isCurrentlyFavorite = isFavorite(fontName);
+  if (isCurrentlyFavorite) {
+    removeFavorite(fontName);
+  } else {
+    addFavorite(fontName);
+  }
+  return !isCurrentlyFavorite;
+}
+
+export function getRecentFonts(): string[] {
+  if (typeof window === 'undefined') return [];
+
+  try {
+    const stored = localStorage.getItem(RECENT_FONTS_KEY);
+    return stored ? JSON.parse(stored) : [];
+  } catch {
+    return [];
+  }
+}
+
+export function addRecentFont(fontName: string): void {
+  let recent = getRecentFonts();
+
+  // Remove if already exists
+  recent = recent.filter(f => f !== fontName);
+
+  // Add to beginning
+  recent.unshift(fontName);
+
+  // Keep only MAX_RECENT items
+  recent = recent.slice(0, MAX_RECENT);
+
+  localStorage.setItem(RECENT_FONTS_KEY, JSON.stringify(recent));
+}