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/converters/pandocService.ts

@@ -0,0 +1,41 @@
+import type { ConversionOptions, ProgressCallback, ConversionResult } from '@/types/conversion';
+
+/**
+ * Convert document using Pandoc (placeholder - not yet implemented)
+ */
+export async function convertWithPandoc(
+  file: File,
+  outputFormat: string,
+  options: ConversionOptions = {},
+  onProgress?: ProgressCallback
+): Promise<ConversionResult> {
+  // TODO: Implement Pandoc WASM conversion when available
+  // For now, return an error
+
+  if (onProgress) onProgress(0);
+
+  return {
+    success: false,
+    error: 'Pandoc WASM converter is not yet implemented. Document conversion coming soon!',
+  };
+}
+
+/**
+ * Convert Markdown to HTML (placeholder)
+ */
+export async function markdownToHtml(
+  file: File,
+  onProgress?: ProgressCallback
+): Promise<ConversionResult> {
+  return convertWithPandoc(file, 'html', {}, onProgress);
+}
+
+/**
+ * Convert HTML to Markdown (placeholder)
+ */
+export async function htmlToMarkdown(
+  file: File,
+  onProgress?: ProgressCallback
+): Promise<ConversionResult> {
+  return convertWithPandoc(file, 'md', {}, onProgress);
+}