Add File model with getFileSizeInMB; pass sizeInStorage to show-documents

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/Models/File.php

@@ -0,0 +1,13 @@
+<?php
+
+namespace App\Models;
+
+class File
+{
+    public static function getFileSizeInMB(int $bytes): string
+    {
+        if ($bytes <= 0) return '0';
+        $mb = $bytes / 1024 / 1024;
+        return number_format($mb, 2);
+    }
+}