refactor(radiogroupnav): remove aria-checked setAttribute calls

The action was writing aria-checked directly and then firing onChange,
which also triggered Svelte's own aria-checked={selected === type} binding.
Double-ownership: action now only calls focus() + onChange(value);
Svelte owns the attribute update.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/shared/actions/radioGroupNav.ts

@@ -18,8 +18,6 @@ export function radioGroupNav(
 		const delta = event.key === 'ArrowRight' ? 1 : -1;
 		const next = (current + delta + radios.length) % radios.length;
 
-		radios[current].setAttribute('aria-checked', 'false');
-		radios[next].setAttribute('aria-checked', 'true');
 		radios[next].focus();
 		onChangeFn?.(radios[next].getAttribute('value') ?? '');
 	}