Simplify Call Screen

Nobody has claimed this yet.

### Your use case

It isn't apparent that the shortcuts on the top right still applies in a call, not simply to start one.
#### What would you like to do?
**1.** Remove the header line.
**2.** Reduce number of shortcuts in call.
- Hide Threads button.
- Hide or remove Room-info button. https://github.com/element-hq/element-web/issues/33586#issue-4499402650

**3.** Add button to hide **other participants** in Spotlight mode (the right pointing arrow in the spotlight tile).
**4.** include 3 dot menu in spotlight tile (bottom right of tile).
- Invert colour scheme to match display-name pill.

**6** Reduce saturation of end-call button https://github.com/element-hq/element-web/issues/34856.
**7.** Replace spotlight and grid toggle with Expand and Full-screen buttons respectively.
- Expand button should hide the room list and expands the call interface into the newly available space.

**8.** Make the expand and grid toggle a single icon toggle and move it to the main cluster of controls. (in the mock up it sits next to the end-call button).

#### Why would you like to do it?
- Reduce visual noise.
- Make the useful shortcuts for a call apparent.
- Reduce visual prominence of the end-call button.
#### How would you like to achieve it?

### Have you considered any alternatives?

> **3.** Add button to hide **other participants** in Spotlight mode (the right pointing arrow in the spotlight tile).
1. Make the arrow white.
2. Adding a background and making the icon black & white like the display-name pill.
- Or white, with translucent black background.

### Additional context

https://github.com/element-hq/element-web/issues/34619#issuecomment-5448529125
https://github.com/element-hq/element-call/issues/4199#issue-5243084405

No files or tests are named. Start by reviewing the attached mockup and the linked Element Call and Element Web issues, then locate the call-screen UI entry point. Done means the requested shortcut, participant, menu, layout, fullscreen, and end-call-button changes are implemented consistently with the stated visual goals.

Written by the indexing model from the issue text.