feat: initialize Convert UI - browser-based file conversion app

- Add Next.js 16 with Turbopack and React 19
- Add Tailwind CSS 4 with OKLCH color system
- Implement FFmpeg.wasm for video/audio conversion
- Implement ImageMagick WASM for image conversion
- Add file upload with drag-and-drop
- Add format selector with fuzzy search
- Add conversion preview and download
- Add conversion history with localStorage
- Add dark/light theme support
- Support 22+ file formats across video, audio, and images

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

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

types/conversion.ts

@@ -0,0 +1,127 @@
+/**
+ * Supported converter engines
+ */
+export type ConverterEngine = 'ffmpeg' | 'imagemagick' | 'pandoc';
+
+/**
+ * File category based on type
+ */
+export type FileCategory = 'video' | 'audio' | 'image' | 'document';
+
+/**
+ * Conversion status
+ */
+export type ConversionStatus = 'pending' | 'loading' | 'processing' | 'completed' | 'error';
+
+/**
+ * Supported conversion format
+ */
+export interface ConversionFormat {
+  id: string;
+  name: string;
+  extension: string;
+  mimeType: string;
+  category: FileCategory;
+  converter: ConverterEngine;
+  description?: string;
+}
+
+/**
+ * Conversion job configuration
+ */
+export interface ConversionJob {
+  id: string;
+  inputFile: File;
+  inputFormat: ConversionFormat;
+  outputFormat: ConversionFormat;
+  options: ConversionOptions;
+  status: ConversionStatus;
+  progress: number;
+  result?: Blob;
+  error?: string;
+  startTime?: number;
+  endTime?: number;
+}
+
+/**
+ * Generic conversion options
+ */
+export interface ConversionOptions {
+  // Video options
+  videoBitrate?: string;
+  videoCodec?: string;
+  videoResolution?: string;
+  videoFps?: number;
+
+  // Audio options
+  audioBitrate?: string;
+  audioCodec?: string;
+  audioSampleRate?: number;
+  audioChannels?: number;
+
+  // Image options
+  imageQuality?: number;
+  imageWidth?: number;
+  imageHeight?: number;
+  imageFormat?: string;
+
+  // Document options
+  documentPageSize?: string;
+  documentMargins?: string;
+  documentStyles?: boolean;
+
+  // Generic options
+  [key: string]: string | number | boolean | undefined;
+}
+
+/**
+ * History item for conversion history
+ */
+export interface ConversionHistoryItem {
+  id: string;
+  inputFileName: string;
+  inputFormat: string;
+  outputFormat: string;
+  outputFileName: string;
+  timestamp: number;
+  fileSize: number;
+  result?: Blob;
+}
+
+/**
+ * Format preset for common conversions
+ */
+export interface FormatPreset {
+  id: string;
+  name: string;
+  description: string;
+  category: FileCategory;
+  sourceFormats: string[];
+  targetFormat: string;
+  options: ConversionOptions;
+  icon?: string;
+}
+
+/**
+ * WASM module loading state
+ */
+export interface WASMModuleState {
+  ffmpeg: boolean;
+  imagemagick: boolean;
+  pandoc: boolean;
+}
+
+/**
+ * Progress callback for conversion
+ */
+export type ProgressCallback = (progress: number) => void;
+
+/**
+ * Conversion result
+ */
+export interface ConversionResult {
+  success: boolean;
+  blob?: Blob;
+  error?: string;
+  duration?: number;
+}