requestFullscreen() on the voice container puts only its descendants in the
browser's top layer; overlays portaled to document.body were rendered outside
that layer and stayed invisible — most visibly the right-click context menu on
stream tiles and voice user panels.
Add usePortalContainer() hook returning document.fullscreenElement ?? document.body
and re-rendering on fullscreenchange. Migrate every overlay reachable during a
call: ContextMenuRenderer (desktop, submenu, mobile sheet), Tooltip,
ConfirmDialog, ConnectionInfoPopover, ScreenShareSettingsPopover, and
ScreenSharePicker (which previously rendered inline at App root).
Jannis Braun
e0861597bc