feat(deadline-banner): auto mode pulls all calendar_items globally

Auto-mode deadline_banner now resolves to the next future event across
all calendar_items in the CMS instead of requiring a manually-curated
items[] pool. Server load hooks (+page.server.ts for /, /[...slug],
/post/[slug]) call resolveDeadlineBannerBlocks which fetches the
global calendar_item list once and attaches it as items[] when mode
is "auto" and items[] is not already resolved. Component logic
unchanged — it still picks the soonest future entry.

Also:
- cms.ts: getCalendarItems() bulk list fetcher
- PostOverviewBlock.svelte: design defaults to "cards" when value is
  empty string (not just null/undefined) so existing entries with
  design: "" render

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/lib/components/ContentRows.svelte

@@ -14,6 +14,7 @@
   import CalendarBlock from "./blocks/CalendarBlock.svelte";
   import OrganisationsBlock from "./blocks/OrganisationsBlock.svelte";
   import OpnFormBlock from "./blocks/OpnFormBlock.svelte";
+  import DeadlineBannerBlock from "./blocks/DeadlineBannerBlock.svelte";
   import { isBlockLayoutBreakout, getSpaceBottomClass } from "$lib/block-layout";
   import type { BlockLayout } from "$lib/block-layout";
   import type { Translations } from "$lib/translations";
@@ -35,6 +36,7 @@
     CalendarBlockData,
     OrganisationsBlockData,
     OpnFormBlockData,
+    DeadlineBannerBlockData,
   } from "$lib/block-types";
 
   let { layout, class: className = "", translations = {} }: { layout: RowContentLayout; class?: string; translations?: Translations | null } = $props();
@@ -128,6 +130,8 @@
                 <OrganisationsBlock block={item as OrganisationsBlockData} />
               {:else if blockType(item) === "opnform"}
                 <OpnFormBlock block={item as OpnFormBlockData} />
+              {:else if blockType(item) === "deadline_banner"}
+                <DeadlineBannerBlock block={item as DeadlineBannerBlockData} />
               {:else}
                 <div class="col-span-12 rounded border border-amber-200 bg-amber-50 px-3 py-2 text-sm text-amber-800">
                   Unbekannter Block: <code>{blockType(item)}</code>