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/converter/FontPreview.tsx

@@ -3,7 +3,7 @@
 import * as React from 'react';
 import { Card } from '@/components/ui/Card';
 import { Button } from '@/components/ui/Button';
-import { Copy, Download } from 'lucide-react';
+import { Copy, Download, Share2 } from 'lucide-react';
 import { cn } from '@/lib/utils/cn';
 
 export interface FontPreviewProps {
@@ -11,10 +11,11 @@ export interface FontPreviewProps {
   isLoading?: boolean;
   onCopy?: () => void;
   onDownload?: () => void;
+  onShare?: () => void;
   className?: string;
 }
 
-export function FontPreview({ text, isLoading, onCopy, onDownload, className }: FontPreviewProps) {
+export function FontPreview({ text, isLoading, onCopy, onDownload, onShare, className }: FontPreviewProps) {
   return (
     <Card className={cn('relative', className)}>
       <div className="p-6">
@@ -27,6 +28,12 @@ export function FontPreview({ text, isLoading, onCopy, onDownload, className }:
                 Copy
               </Button>
             )}
+            {onShare && (
+              <Button variant="outline" size="sm" onClick={onShare} title="Copy shareable URL">
+                <Share2 className="h-4 w-4" />
+                Share
+              </Button>
+            )}
             {onDownload && (
               <Button variant="outline" size="sm" onClick={onDownload}>
                 <Download className="h-4 w-4" />