Web: Chat > Right panel > Remove left/right padding from call banners in the timeline

### Description of problem

When on a call and the chat is open in the right panel, a call banner in the timeline should fill the horizontal space. Currently there is extra space on the right & left, leaving very little room for any content. It should look like this:

Meanwhile, the extra spacing is fine in the regular timeline (when not on a call) because there's a lot more space for content.

Start by reproducing the issue in Element Web with a call active and Chat open in the right panel, then inspect the call banner component and its styling. Remove the left and right spacing only for banners in the right-panel timeline, while retaining the existing spacing in the regular timeline. Verify both layouts visually.

Written by the indexing model from the issue text.