feat(section-grid): InfoCard + SectionGrid als CMS-Block

Neuer section_grid-Block (SectionHeader + Card-Grid aus info_card-Refs) +
info_card-Collection. SectionGrid/InfoCard-Komponenten, BlockRenderer-Case,
content_layout erlaubt section_grid in Rows. SectionHeader.title jetzt optional
(Kicker-only-Header).

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

src/lib/components/SectionHeader.svelte

@@ -13,7 +13,7 @@
   let {
     number = undefined,
     kicker = undefined,
-    title,
+    title = undefined,
     subtitle = undefined,
     actionLabel = undefined,
     actionHref = undefined,
@@ -22,7 +22,7 @@
   }: {
     number?: string;              // z. B. "03" — tabular-nums, wald-500
     kicker?: string;              // Label, uppercase — optional (CMS-Blocks liefern oft nur title)
-    title: string;
+    title?: string;              // optional — z.B. Kicker-only-Header (nur "01 · DIREKTER DRAHT")
     subtitle?: string;
     actionLabel?: string;
     actionHref?: string;
@@ -51,10 +51,12 @@
       </div>
     {/if}
 
-    <!-- Titel (\n → harter Umbruch, wie HeadlineBlock) -->
-    <svelte:element this={tag} class="text-3xl font-bold tracking-[-0.02em] text-stein-800 lg:text-[34px]">
-      {#each title.split('\n') as line, i}{#if i > 0}<br />{/if}{line}{/each}
-    </svelte:element>
+    <!-- Titel (\n → harter Umbruch, wie HeadlineBlock). Optional — Kicker-only-Header. -->
+    {#if title}
+      <svelte:element this={tag} class="text-3xl font-bold tracking-[-0.02em] text-stein-800 lg:text-[34px]">
+        {#each title.split('\n') as line, i}{#if i > 0}<br />{/if}{line}{/each}
+      </svelte:element>
+    {/if}
 
     {#if subtitle}
       <p class="mt-2 text-base text-stein-500">{subtitle}</p>