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>

lib/utils/fileUtils.ts

@@ -0,0 +1,95 @@
+/**
+ * Format file size in human-readable format
+ */
+export function formatFileSize(bytes: number): string {
+  if (bytes === 0) return '0 Bytes';
+
+  const k = 1024;
+  const sizes = ['Bytes', 'KB', 'MB', 'GB'];
+  const i = Math.floor(Math.log(bytes) / Math.log(k));
+
+  return `${Math.round(bytes / Math.pow(k, i) * 100) / 100} ${sizes[i]}`;
+}
+
+/**
+ * Validate file size (max 500MB for browser processing)
+ */
+export function validateFileSize(file: File, maxSizeMB: number = 500): boolean {
+  const maxBytes = maxSizeMB * 1024 * 1024;
+  return file.size <= maxBytes;
+}
+
+/**
+ * Get file extension from filename
+ */
+export function getFileExtension(filename: string): string {
+  const lastDot = filename.lastIndexOf('.');
+  return lastDot === -1 ? '' : filename.substring(lastDot + 1).toLowerCase();
+}
+
+/**
+ * Get filename without extension
+ */
+export function getFilenameWithoutExtension(filename: string): string {
+  const lastDot = filename.lastIndexOf('.');
+  return lastDot === -1 ? filename : filename.substring(0, lastDot);
+}
+
+/**
+ * Generate output filename
+ */
+export function generateOutputFilename(inputFilename: string, outputExtension: string): string {
+  const basename = getFilenameWithoutExtension(inputFilename);
+  return `${basename}.${outputExtension}`;
+}
+
+/**
+ * Download blob as file
+ */
+export function downloadBlob(blob: Blob, filename: string): void {
+  const url = URL.createObjectURL(blob);
+  const a = document.createElement('a');
+  a.href = url;
+  a.download = filename;
+  document.body.appendChild(a);
+  a.click();
+  document.body.removeChild(a);
+  URL.revokeObjectURL(url);
+}
+
+/**
+ * Read file as ArrayBuffer
+ */
+export async function readFileAsArrayBuffer(file: File): Promise<ArrayBuffer> {
+  return new Promise((resolve, reject) => {
+    const reader = new FileReader();
+    reader.onload = () => resolve(reader.result as ArrayBuffer);
+    reader.onerror = () => reject(reader.error);
+    reader.readAsArrayBuffer(file);
+  });
+}
+
+/**
+ * Read file as Data URL
+ */
+export async function readFileAsDataURL(file: File): Promise<string> {
+  return new Promise((resolve, reject) => {
+    const reader = new FileReader();
+    reader.onload = () => resolve(reader.result as string);
+    reader.onerror = () => reject(reader.error);
+    reader.readAsDataURL(file);
+  });
+}
+
+/**
+ * Validate file type against allowed MIME types
+ */
+export function validateFileType(file: File, allowedTypes: string[]): boolean {
+  return allowedTypes.some((type) => {
+    if (type.endsWith('/*')) {
+      const category = type.split('/')[0];
+      return file.type.startsWith(`${category}/`);
+    }
+    return file.type === type;
+  });
+}