Outputs: Say the menus are on the device, instead of showing black

When no screen on the stack shows anything on an output (we're in the
menus), the background screen draws "Menus are on your device" there.
UI drawn to an output gets the primary's DPI scale, over the whole output.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

UI/MiscScreens.cpp

@@ -97,6 +97,20 @@ void HandleCommonMessages(UIMessage message, const char *value, ScreenManager *m
 	}
 }
 
+// Nothing on the stack shows anything there, so we're in the menus.
+bool BackgroundScreen::renderOutput(const OutputDisplay &output) {
+	if (output.role != OutputRole::Game) {
+		return false;
+	}
+	UIContext &dc = *screenManager()->getUIContext();
+	auto di = GetI18NCategory(I18NCat::DIALOG);
+	const Bounds &bounds = dc.GetBounds();
+	dc.Begin();
+	dc.DrawText(di->T("Menus are on your device"), bounds.centerX(), bounds.centerY(), 0xFF505050, ALIGN_CENTER);
+	dc.Flush();
+	return true;
+}
+
 ScreenRenderFlags BackgroundScreen::render(ScreenRenderMode mode) {
 	UIContext *uiContext = screenManager()->getUIContext();