Add screencast-only fullscreen mode for group call screenshare

Introduce a dedicated fullscreen toggle in wide controls for screenshare.

When a screen endpoint is focused, fullscreen can now switch to a screencast-only layout that hides side panels. Fullscreen controls in this mode auto-hide on inactivity and reappear on mouse movement.

Also disable speaking outline rendering in fullscreen to avoid full-frame green highlighting tied to members panel speaking state.

Author: paterkleomenis

Telegram/SourceFiles/calls/calls.style

@@ -1008,6 +1008,22 @@ groupCallScreenShareSmall: CallButton(groupCallSettingsSmall) {
 		rippleAreaPosition: point(8px, 12px);
 	}
 }
+groupCallFullScreenSmall: CallButton(groupCallSettingsSmall) {
+	button: IconButton(groupCallSettingsInner) {
+		icon: callMuteToFullScreen;
+		width: 60px;
+		height: 68px;
+		rippleAreaPosition: point(8px, 12px);
+	}
+}
+groupCallFullScreenActiveSmall: CallButton(groupCallFullScreenSmall) {
+	button: IconButton(groupCallSettingsInner) {
+		icon: callMuteFromFullScreen;
+		width: 60px;
+		height: 68px;
+		rippleAreaPosition: point(8px, 12px);
+	}
+}
 groupCallMenuToggleSmall: CallButton(groupCallSettingsSmall) {
 	button: IconButton(groupCallSettingsInner) {
 		icon: icon {{ "calls/calls_more", groupCallIconFg }};