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/CreateElement/CreateElementRequest.php

@@ -10,7 +10,8 @@ class CreateElementRequest
         public ?string $description,
         public ?string $iconImageUrl,
         public ?string $richText,
-        public ?string $pdfPath,
+        public ?string $shortPdfPath,
+        public ?string $longPdfPath,
         public ?string $youtubeUrl,
         public ?int $parentElementId,
     ) {