feat: align conversion history width with upload container

Added max-w-4xl container constraint to ConversionHistory component to match
the FileConverter component width, creating a more consistent and aligned layout.

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

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

components/converter/ConversionHistory.tsx

@@ -71,6 +71,7 @@ export function ConversionHistory() {
 
   if (history.length === 0) {
     return (
+      <div className="w-full max-w-4xl mx-auto">
         <Card>
           <CardHeader>
             <CardTitle className="flex items-center gap-2">
@@ -87,10 +88,12 @@ export function ConversionHistory() {
             </div>
           </CardContent>
         </Card>
+      </div>
     );
   }
 
   return (
+    <div className="w-full max-w-4xl mx-auto">
       <Card>
         <CardHeader>
           <div className="flex items-center justify-between">
@@ -165,5 +168,6 @@ export function ConversionHistory() {
           </div>
         </CardContent>
       </Card>
+    </div>
   );
 }