Add centralized saveMedia helpers for image, video, and file downloads.

Platforms can register a custom saver; viewers share one download/save path instead of FileSaver call sites.

src/app/components/message/content/FileContent.tsx

@@ -1,8 +1,8 @@
 import React, { ReactNode, useCallback, useState } from 'react';
 import { Box, Button, Modal, Overlay, OverlayBackdrop, OverlayCenter, Spinner, Text, Tooltip, TooltipProvider, as } from 'folds';
 import { Icon, Icons } from '../../icons';
-import FileSaver from 'file-saver';
 import { EncryptedAttachmentInfo } from 'browser-encrypt-attachment';
+import { saveMediaBlob } from '../../../utils/saveMedia';
 import FocusTrap from 'focus-trap-react';
 import { IFileInfo } from '../../../../types/matrix/common';
 import { AsyncStatus, useAsyncCallback } from '../../../hooks/useAsyncCallback';
@@ -252,9 +252,8 @@ export function DownloadFile({ body, mimeType, url, info, encInfo }: DownloadFil
         ? await downloadEncryptedMedia(mediaUrl, (encBuf) => decryptFile(encBuf, mimeType, encInfo), accessToken)
         : await downloadMedia(mediaUrl, accessToken);
 
-      const fileURL = URL.createObjectURL(fileContent);
-      FileSaver.saveAs(fileURL, body);
-      return fileURL;
+      await saveMediaBlob(fileContent, body);
+      return fileContent;
     }, [mx, url, useAuthentication, mimeType, encInfo, body])
   );
 
@@ -268,7 +267,7 @@ export function DownloadFile({ body, mimeType, url, info, encInfo }: DownloadFil
       size="400"
       onClick={() =>
         downloadState.status === AsyncStatus.Success
-          ? FileSaver.saveAs(downloadState.data, body)
+          ? saveMediaBlob(downloadState.data, body)
           : download()
       }
       disabled={downloadState.status === AsyncStatus.Loading}