Allow calls to display edge-to-edge on mobile

By adding viewport-fit=cover to the <meta name="viewport"> header, the page now requests to be displayed edge-to-edge across the entire screen. This gives us control over what we display around camera cut-outs and system navigation UI, if the user agent supports it. I then adjusted the styles of various UI elements to ensure that they still lie within the screen's safe area.

src/components/CallFooter.stories.tsx

@@ -157,6 +157,8 @@ export const UnavailableMediaDevices: Story = {
   ...Default,
   args: {
     ...Default.args,
+    audioEnabled: false,
+    videoEnabled: false,
     toggleAudio: undefined,
     toggleVideo: undefined,
     audioOutputSwitcher: undefined,