Fix fetch body handling for FileUpload objects in uploadToStorage

Restore the original conditional logic to properly handle both File and FileUpload types.
- File objects extend Blob and can be passed directly to fetch
- FileUpload objects need .stream() called to get a ReadableStream for the fetch body
- Added type assertion to help TypeScript with type narrowing

This fixes the misleading type signature where File | FileUpload is accepted
but only File was being handled correctly.

Author: cursoragent

app/utils/storage.server.ts

@@ -14,7 +14,7 @@ async function uploadToStorage(file: File | FileUpload, key: string) {
 	const uploadResponse = await fetch(url, {
 		method: 'PUT',
 		headers,
-		body: file,
+		body: file instanceof File ? file : (file as FileUpload).stream(),
 	})
 
 	if (!uploadResponse.ok) {