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/UpdateIconImageRequest.php

@@ -6,10 +6,10 @@ class UpdateIconImageRequest
 {
     public function __construct(
         public ?int $id,
-        public ?string $iconImageContents,
-        public ?string $iconImageOriginalName,
-        public ?string $iconImageMimeType,
-        public ?int $iconImageSizeBytes,
+        public ?string $fileContents,
+        public ?string $fileOriginalName,
+        public ?string $fileMimeType,
+        public ?int $fileSizeBytes,
     ) {
     }
 }