fix(a11y): add role="note" to JourneyInterlude so aria-label is announced

Without a landmark or widget role, aria-label on a generic <div> is
silently ignored by most screen readers (ARIA spec). Adding role="note"
gives the element an ARIA role that accepts an accessible name, making
the interlude label actually announced.

Also adds a test asserting role="note" and the matching aria-label are
both present on the same element.

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

frontend/src/lib/geschichte/JourneyInterlude.svelte

@@ -9,6 +9,7 @@ let { note }: Props = $props();
 </script>
 
 <div
+	role="note"
 	aria-label={m.journey_interlude_aria_label()}
 	class="my-2 border-l-4 border-journey-border bg-journey-tint px-4 py-3"
 >