Remove full screen button from PiP view

### Your use case

From a PIP window you can make the call window full screen with the button on the bottom right.
But there isn't a button to undo the change in grid view.

This is fine for when you're in the room since you must select "Spotlight" to see the maximise button and the subsequent minimise button when in full screen.

When maximising from PiP the minimise button is not apparent.

#### What would you like to do?
Add maximise/minimise button to grid view

### Have you considered any alternatives?

_No response_

### Additional context

_No response_

No file or test is named. Start by tracing the PiP window and grid-view controls in the frontend, then compare how maximise and minimise actions are exposed in each view. Done means the grid view provides an apparent way to maximise and undo that change, matching the intended PiP behavior.

Written by the indexing model from the issue text.