feat: add format presets for common conversion scenarios

Format presets included:
**Video Presets:**
- YouTube Video (1080p, H.264, optimized)
- Instagram Video (Square format, 1:1)
- Twitter Video (720p, small file)
- Web Optimized (Streaming, low bitrate)

**Audio Presets:**
- Podcast (MP3, voice optimized, 128k)
- High Quality Music (MP3, 320k)
- Audiobook (Mono, 64k, small size)

**Image Presets:**
- Web Thumbnail (JPG, 800px width)
- HD Image (PNG, lossless, high quality)
- Social Media (JPG, 1200px, optimized)
- Web Optimized (WebP, small size)

Implementation:
- Created formatPresets.ts with 11 predefined presets
- FormatPresets component with responsive grid layout
- One-click preset application
- Automatically configures format and options
- Toast notification on preset selection
- Visual feedback with ring highlight
- Organized by category (video/audio/image)
- Emoji icons for visual appeal

User experience:
- Quick access to common conversion scenarios
- No need to manually configure complex settings
- Preset descriptions explain use case
- Disabled during active conversion
- Clear visual indication of selected preset

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

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

lib/utils/formatPresets.ts

@@ -0,0 +1,188 @@
+import type { ConversionOptions } from '@/types/conversion';
+
+export interface FormatPreset {
+  id: string;
+  name: string;
+  description: string;
+  icon: string;
+  category: 'video' | 'audio' | 'image';
+  outputFormat: string;
+  options: ConversionOptions;
+}
+
+/**
+ * Predefined format presets for common use cases
+ */
+export const FORMAT_PRESETS: FormatPreset[] = [
+  // Video Presets
+  {
+    id: 'youtube-video',
+    name: 'YouTube Video',
+    description: '1080p MP4, optimized for YouTube',
+    icon: '🎬',
+    category: 'video',
+    outputFormat: 'mp4',
+    options: {
+      videoCodec: 'libx264',
+      videoBitrate: '5M',
+      videoResolution: '1920x-1',
+      videoFps: 30,
+      audioCodec: 'aac',
+      audioBitrate: '192k',
+    },
+  },
+  {
+    id: 'instagram-video',
+    name: 'Instagram Video',
+    description: 'Square 1:1 format for Instagram',
+    icon: '📸',
+    category: 'video',
+    outputFormat: 'mp4',
+    options: {
+      videoCodec: 'libx264',
+      videoBitrate: '3M',
+      videoResolution: '1080x-1', // Will be cropped to square
+      videoFps: 30,
+      audioCodec: 'aac',
+      audioBitrate: '128k',
+    },
+  },
+  {
+    id: 'twitter-video',
+    name: 'Twitter Video',
+    description: '720p, optimized for Twitter',
+    icon: '🐦',
+    category: 'video',
+    outputFormat: 'mp4',
+    options: {
+      videoCodec: 'libx264',
+      videoBitrate: '2M',
+      videoResolution: '1280x-1',
+      videoFps: 30,
+      audioCodec: 'aac',
+      audioBitrate: '128k',
+    },
+  },
+  {
+    id: 'web-video',
+    name: 'Web Optimized',
+    description: 'Small file size for web streaming',
+    icon: '🌐',
+    category: 'video',
+    outputFormat: 'mp4',
+    options: {
+      videoCodec: 'libx264',
+      videoBitrate: '1.5M',
+      videoResolution: '854x-1',
+      videoFps: 24,
+      audioCodec: 'aac',
+      audioBitrate: '96k',
+    },
+  },
+
+  // Audio Presets
+  {
+    id: 'podcast-audio',
+    name: 'Podcast',
+    description: 'MP3, optimized for voice',
+    icon: '🎙️',
+    category: 'audio',
+    outputFormat: 'mp3',
+    options: {
+      audioCodec: 'libmp3lame',
+      audioBitrate: '128k',
+      audioSampleRate: 44100,
+      audioChannels: 2,
+    },
+  },
+  {
+    id: 'music-high-quality',
+    name: 'High Quality Music',
+    description: 'MP3, 320kbps for music',
+    icon: '🎵',
+    category: 'audio',
+    outputFormat: 'mp3',
+    options: {
+      audioCodec: 'libmp3lame',
+      audioBitrate: '320k',
+      audioSampleRate: 48000,
+      audioChannels: 2,
+    },
+  },
+  {
+    id: 'audiobook',
+    name: 'Audiobook',
+    description: 'Mono, small file size',
+    icon: '📚',
+    category: 'audio',
+    outputFormat: 'mp3',
+    options: {
+      audioCodec: 'libmp3lame',
+      audioBitrate: '64k',
+      audioSampleRate: 22050,
+      audioChannels: 1,
+    },
+  },
+
+  // Image Presets
+  {
+    id: 'web-thumbnail',
+    name: 'Web Thumbnail',
+    description: 'JPG, 800px width, optimized',
+    icon: '🖼️',
+    category: 'image',
+    outputFormat: 'jpg',
+    options: {
+      imageQuality: 85,
+      imageWidth: 800,
+    },
+  },
+  {
+    id: 'hd-image',
+    name: 'HD Image',
+    description: 'PNG, high quality, lossless',
+    icon: '🎨',
+    category: 'image',
+    outputFormat: 'png',
+    options: {
+      imageQuality: 100,
+    },
+  },
+  {
+    id: 'social-media-image',
+    name: 'Social Media',
+    description: 'JPG, 1200px, optimized',
+    icon: '📱',
+    category: 'image',
+    outputFormat: 'jpg',
+    options: {
+      imageQuality: 90,
+      imageWidth: 1200,
+    },
+  },
+  {
+    id: 'web-optimized-image',
+    name: 'Web Optimized',
+    description: 'WebP, small file size',
+    icon: '⚡',
+    category: 'image',
+    outputFormat: 'webp',
+    options: {
+      imageQuality: 80,
+    },
+  },
+];
+
+/**
+ * Get presets by category
+ */
+export function getPresetsByCategory(category: 'video' | 'audio' | 'image'): FormatPreset[] {
+  return FORMAT_PRESETS.filter(preset => preset.category === category);
+}
+
+/**
+ * Get preset by ID
+ */
+export function getPresetById(id: string): FormatPreset | undefined {
+  return FORMAT_PRESETS.find(preset => preset.id === id);
+}