Can't tell when other people have video muted

### Steps to reproduce

1. Join conf
2. Half the squares are grey
3. You can't tell whether they're grey because the sender has turned off their camera, or because of a bug.

### Outcome

#### What did you expect?

Show a video mute icon if someone is not sending video.

#### What happened instead?

No video mute icon; much grey.

### Operating system

_No response_

### Browser information

_No response_

### URL for webapp

_No response_

### Will you send logs?

No

Start by joining a conference and inspecting the participant squares when a sender is not sending video. Trace how that video state is represented in the participant tile UI. Done means a video mute icon distinguishes an intentionally absent video feed from an unexplained grey tile.

Written by the indexing model from the issue text.