Show spinner on remote tiles

When connection to a remote member's transport is lost **or** we're unable to decrypt their media, show a spinner on the name tag of their user media tiles:

https://www.figma.com/design/aOEkaJtaBmPy058V7uoqVr/Element-Call-Updates---2026?node-id=1391-53523&t=cZED3OTPOsXb0wy7-4

This should replace the "waiting for media" overlay.

In cases where there is no name tag, it should look like this:

https://www.figma.com/design/aOEkaJtaBmPy058V7uoqVr/Element-Call-Updates---2026?node-id=1426-13012&t=ae2fanXuOQlg58sd-4

Start by locating the user media tile and existing “waiting for media” overlay, then trace how lost remote transport and media decryption failures reach that UI. Compare the linked Figma designs for tiles with and without a name tag; done means the spinner replaces the overlay in both cases.

Written by the indexing model from the issue text.