Simplify beforeunload handler

Remove unnecessary comments and custom message strings. The handler
now simply triggers the browser's confirmation dialog for temporary sites.

Author: jnealey88

packages/playground/website/src/lib/state/redux/slice-ui.ts

@@ -137,16 +137,15 @@ export const browserConfirmationMiddleware: Middleware =
 					const state = store.getState() as any;
 					// Access the active site directly from state structure
 					const activeSiteSlug = state.ui?.activeSite?.slug;
-					const activeSite = activeSiteSlug ? state.sites?.entities?.[activeSiteSlug] : undefined;
-					
+					const activeSite = activeSiteSlug
+						? state.sites?.entities?.[activeSiteSlug]
+						: undefined;
+
 					// Only show confirmation for temporary sites (storage === 'none')
 					if (activeSite && activeSite.metadata?.storage === 'none') {
-						const message = 'Your changes will be lost. This is a temporary Playground site. Are you sure you want to leave?';
 						e.preventDefault();
-						// Modern browsers require setting returnValue
-						e.returnValue = message;
-						// Some older browsers use the return value
-						return message;
+						e.returnValue = '';
+						return '';
 					}
 				});
 			}