feat(layout): add global announcement banner above nav

Adds AnnouncementBanner component fed by a new top_banner CMS entry
(site-announcement). Extended top_banner schema and TS types with
optional link + linkLabel fields. Rendered inline-markdown text.

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

src/routes/+layout.server.ts

@@ -15,6 +15,7 @@ import type {
   NavigationEntry,
   FooterEntry,
   PageConfigEntry,
+  TopBannerEntry,
 } from '$lib/cms';
 import { ensureTransformedImage } from '$lib/rusty-image';
 import {
@@ -84,6 +85,7 @@ export const load: LayoutServerLoad = async ({ locals, route }) => {
   let bootstrapNavSocial: NavigationEntry | null = null;
   let bootstrapFooter: FooterEntry | null = null;
   let bootstrapConfig: PageConfigEntry | null = null;
+  let bootstrapTopBanner: TopBannerEntry | null = null;
   try {
     const batch = await batchFetch([
       {
@@ -114,11 +116,17 @@ export const load: LayoutServerLoad = async ({ locals, route }) => {
         locale: 'de',
         resolve: 'logo',
       },
+      {
+        id: 'topBanner',
+        collection: 'top_banner',
+        slug: 'site-announcement',
+      },
     ]);
     bootstrapNavHeader = batchData<NavigationEntry>(batch.results.navHeader);
     bootstrapNavSocial = batchData<NavigationEntry>(batch.results.navSocial);
     bootstrapFooter = batchData<FooterEntry>(batch.results.footer);
     bootstrapConfig = batchData<PageConfigEntry>(batch.results.config);
+    bootstrapTopBanner = batchData<TopBannerEntry>(batch.results.topBanner);
   } catch (err) {
     /* CMS nicht erreichbar — alle Felder bleiben null, Page rendert ohne. */
     logWarn('layout.bootstrap', err);
@@ -328,5 +336,6 @@ export const load: LayoutServerLoad = async ({ locals, route }) => {
     seoDescriptionTemplate: pageConfig?.seoDescription ?? null,
     analyticsPm86SiteId:
       (pageConfig as { analyticsPm86SiteId?: string } | null)?.analyticsPm86SiteId ?? null,
+    announcementBanner: bootstrapTopBanner,
   };
 };