End a private match from End Game and return to the lobby

The Yes button of the pause menu's End Game popup is rewritten to
`disconnect` (03016c48). The host of a private match therefore quits
instead of ending the match: nobody sees the "Host ended game"
end-of-match flow, and the host lands on the main menu with the lobby
gone.

The button now sends the "endround" menu response to the game scripts,
which end the match as host-ended, run the end-of-game display and then
end the level, so the host returns to the private lobby. The hud still
turns that response into `disconnect` unless the local player hosts a
private lobby (ui_lobby_host set, ui_lobby_public not set), so public
lobbies and clients leave as they do today.

This reverses the end-game leave from 03016c48 for private hosts only.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/GSC-RUNTIME.md

@@ -373,9 +373,9 @@ record is imported or initialized.
 ## Remaining
 
 A live bomb plant/defuse check. Native IW4L menus can create a private lobby,
-select a map/mode and start a match. When the match scripts end it, the host
-returns to the same private lobby with map, mode and rules kept, as it does when
-the map fails to load. A disconnect, including End Game from the pause menu,
+select a map/mode and start a match. When the match scripts end it, or the host
+picks End Game from the pause menu, the host returns to the same private lobby with
+map, mode and rules kept, as it does when the map fails to load. A disconnect
 returns to the main menu. Browser/public-lobby
 actions are connected but still need multiplayer validation. Display mode/resolution, brightness, volume, VSync, shadows, depth of field and
 bloom are bound to runtime settings and persisted locally. Surround output, voice/chat