feat(frist): Deadline-Banner im AnnouncementBanner-Look (rot), nur ein Balken

- Look wie AnnouncementBanner: kompakte zentrierte Leiste, weiße Schrift, 0.7rem,
  variant-Farbe (urgent=rot), flex-wrap → fließt/stackt sauber mobil
- Countdown als dunkles Badge (bg-black/20)
- Layout: aktive Frist verdrängt NEU-Banner → nie 2 Balken über der Navi

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/routes/+layout.svelte

@@ -26,6 +26,19 @@
    */
   const isEmbed = $derived(($page.route.id ?? '').startsWith('/(embed)'));
 
+  // Nur EIN Balken über der Navi: aktive Frist hat Vorrang, sonst NEU-Banner.
+  const deadlineActive = $derived.by(() => {
+    const b = data.deadlineBanner as { mode?: string; date?: string; items?: unknown[] } | null;
+    if (!b) return false;
+    if (b.mode === 'auto') return (b.items ?? []).length > 0;
+    if (!b.date) return false;
+    const d = new Date(b.date);
+    if (Number.isNaN(d.getTime())) return false;
+    const today = new Date(); today.setHours(0, 0, 0, 0);
+    const t = new Date(d); t.setHours(0, 0, 0, 0);
+    return t.getTime() >= today.getTime();
+  });
+
   // Live-preview reload bridge: when the page was loaded with
   // `?preview_draft=...`, accept `rustycms:reload` postMessage events from the
   // admin iframe parent and re-run the SvelteKit `load()` so the iframe
@@ -329,10 +342,9 @@
       class="sr-only focus:not-sr-only focus:fixed focus:top-2 focus:left-2 focus:z-[100] focus:bg-white focus:px-3 focus:py-2 focus:shadow focus:outline focus:outline-2 focus:outline-wald-600 focus:rounded-xs"
     >Zum Inhalt springen</a>
     <div class="flex min-h-screen flex-col text-stein-900">
-      {#if data.deadlineBanner}
+      {#if deadlineActive && data.deadlineBanner}
         <DeadlineBannerBlock block={data.deadlineBanner} />
-      {/if}
-      {#if data.announcementBanner}
+      {:else if data.announcementBanner}
         <AnnouncementBanner banner={data.announcementBanner} />
       {/if}
       {#if pageData?.preview || pageData?.previewDraft}