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/CreateElementDto.php

@@ -12,7 +12,8 @@ class CreateElementDto
         public string $description,
         public ?string $iconImageUrl,
         public string $richText,
-        public ?string $pdfPath,
+        public ?string $shortPdfPath,
+        public ?string $longPdfPath,
         public ?string $youtubeUrl,
         public ?Element $parentElement,
     ) {