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/storage/history.ts

@@ -0,0 +1,85 @@
+import type { ConversionHistoryItem } from '@/types/conversion';
+
+const HISTORY_KEY = 'convert-ui-history';
+const MAX_HISTORY_ITEMS = 10;
+
+/**
+ * Get conversion history from localStorage
+ */
+export function getHistory(): ConversionHistoryItem[] {
+  if (typeof window === 'undefined') return [];
+
+  try {
+    const stored = localStorage.getItem(HISTORY_KEY);
+    if (!stored) return [];
+
+    const history = JSON.parse(stored);
+    return Array.isArray(history) ? history : [];
+  } catch (error) {
+    console.error('Failed to load history:', error);
+    return [];
+  }
+}
+
+/**
+ * Add item to conversion history
+ */
+export function addToHistory(item: Omit<ConversionHistoryItem, 'id' | 'timestamp'>): void {
+  if (typeof window === 'undefined') return;
+
+  try {
+    const history = getHistory();
+
+    const newItem: ConversionHistoryItem = {
+      ...item,
+      id: Math.random().toString(36).substring(7),
+      timestamp: Date.now(),
+    };
+
+    // Add to beginning of array
+    history.unshift(newItem);
+
+    // Keep only the latest MAX_HISTORY_ITEMS
+    const trimmed = history.slice(0, MAX_HISTORY_ITEMS);
+
+    localStorage.setItem(HISTORY_KEY, JSON.stringify(trimmed));
+  } catch (error) {
+    console.error('Failed to save history:', error);
+  }
+}
+
+/**
+ * Clear all conversion history
+ */
+export function clearHistory(): void {
+  if (typeof window === 'undefined') return;
+
+  try {
+    localStorage.removeItem(HISTORY_KEY);
+  } catch (error) {
+    console.error('Failed to clear history:', error);
+  }
+}
+
+/**
+ * Remove single item from history
+ */
+export function removeHistoryItem(id: string): void {
+  if (typeof window === 'undefined') return;
+
+  try {
+    const history = getHistory();
+    const filtered = history.filter((item) => item.id !== id);
+    localStorage.setItem(HISTORY_KEY, JSON.stringify(filtered));
+  } catch (error) {
+    console.error('Failed to remove history item:', error);
+  }
+}
+
+/**
+ * Get history item by ID
+ */
+export function getHistoryItem(id: string): ConversionHistoryItem | undefined {
+  const history = getHistory();
+  return history.find((item) => item.id === id);
+}