[Bug] All media uploads fail with "TauriInvokeError: relay returned 401 Unauthorized: authentication failed"

What I did:
Tried uploading images in two separate contexts:

Setting a new profile avatar (Settings → Identity → avatar upload)
Attaching an image to a chat message (paperclip icon in message composer)

Expected result:
Image uploads successfully in both cases.

Actual result:
Both fail immediately with: TauriInvokeError: relay returned 401 Unauthorized: authentication failed

Steps to reproduce:

Open Buzz Desktop, go to any channel
Click the paperclip/attach icon in the message composer
Select an image
Error appears: TauriInvokeError: relay returned 401 Unauthorized: authentication failed
Same error reproduces when uploading via Settings → avatar

Troubleshooting already tried (ruled out):

System clock is set to auto-sync — not a clock drift issue
No VPN/proxy in use — not a network routing issue
(add here if you also tried logging out/rejoining the community)

Environment:

Buzz version: (fill in — Settings → About)
OS: (Windows/macOS/Linux + version)
Community: self-hosted or buzz.xyz hosted?

Evidence:
(attach both screenshots — avatar upload + chat attachment)

Start with the desktop avatar and chat attachment upload entry points and trace the Tauri relay request that returns 401 Unauthorized. Compare authentication handling for both flows and reproduce the failure in each; done means images upload successfully for avatars and chat attachments.

Written by the indexing model from the issue text.