route element file uploads

Add short and long PDF paths to elements, keep pdfPath as a short PDF compatibility alias, and route generic file uploads by fileType.

backend/app/Element/UseCases/UpdateElement/UpdateShortPdfRequest.php

@@ -0,0 +1,15 @@
+<?php
+
+namespace App\Element\UseCases\UpdateElement;
+
+class UpdateShortPdfRequest
+{
+    public function __construct(
+        public ?int $id,
+        public ?string $fileContents,
+        public ?string $fileOriginalName,
+        public ?string $fileMimeType,
+        public ?int $fileSizeBytes,
+    ) {
+    }
+}