feat(design-system): Storybook + Button-Atom-Vereinheitlichung + SectionHeader

Storybook (SvelteKit-Framework, Tailwind v4, MSW, Translation-Decorator):
Stories für Atoms/Molecules/Organisms + alle CMS-Blocks.

Button-Atom: 5 .btn-*-Varianten (primary/secondary/tertiary/outline/warning),
class-Merge-Prop, href→<a>, Loading-Spinner neben Label, rounded-md/font-medium.
Alle rohen .btn-*- und Hand-Style-Buttons app-weit aufs Atom migriert.

SectionHeader-Molecule (kicker/number/title/subtitle/action) + Integration in
7 CMS-Blocks (post_overview, organisations, organisations_map, searchable_text,
image_gallery, youtube_video_gallery, files) via neuem section_header-Schema.

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

src/lib/components/blocks/OrganisationsBlock.svelte

@@ -9,6 +9,7 @@
   import Badge from "$lib/components/Badge.svelte";
   import RustyImage from "$lib/components/RustyImage.svelte";
   import Button from "$lib/ui/Button.svelte";
+  import SectionHeader from "$lib/components/SectionHeader.svelte";
 
   function organisationLogoField(o: OrganisationEntry) {
     return extractCmsImageField(o.logo);
@@ -22,6 +23,9 @@
   }
 
   let { block }: { block: OrganisationsBlockData } = $props();
+  const actionRef = $derived(
+    block.action && typeof block.action === "object" ? block.action : null,
+  );
 
   const layoutClasses = $derived(
     block.layout ? getBlockLayoutClasses(block.layout) : "col-span-12 mb-4",
@@ -163,9 +167,20 @@
 
 <div class={layoutClasses} data-block="Organisations" data-block-type="organisations" data-block-slug={block._slug}>
   {#if block.headline}
-    <h3
-      class={compact ? "mb-2 text-lg font-semibold text-stein-900" : "mb-4"}
-    >{block.headline}</h3>
+    {#if compact}
+      <h3 class="mb-2 text-lg font-semibold text-stein-900">{block.headline}</h3>
+    {:else}
+      <div class="mb-4">
+        <SectionHeader
+          number={block.number}
+          kicker={block.kicker}
+          title={block.headline}
+          tag="h3"
+          actionLabel={actionRef?.linkName}
+          actionHref={actionRef?.url}
+        />
+      </div>
+    {/if}
   {/if}
 
   {#if carousel}