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/TopBanner.stories.ts

@@ -0,0 +1,31 @@
+import type { Meta, StoryObj } from '@storybook/sveltekit';
+import TopBanner from './TopBanner.svelte';
+
+// Vollbreiter Seiten-Header mit Bild + Headline. `resolvedImages` = fertige
+// Bild-URL(s); läuft über den /cms-images-Proxy.
+const CMS_ASSET =
+  'https://cms.pm86.de/api/assets/pages/img_2814-ar4x2.webp?_environment=windwiderstand';
+
+const meta = {
+  title: 'Organisms/TopBanner',
+  component: TopBanner,
+  tags: ['autodocs'],
+  parameters: { layout: 'fullscreen' },
+} satisfies Meta<typeof TopBanner>;
+
+export default meta;
+type Story = StoryObj<typeof meta>;
+
+export const MitBild: Story = {
+  args: {
+    banner: null,
+    resolvedImages: [CMS_ASSET],
+    focalCss: '50% 40%',
+    headline: 'Wald statt Windkraft',
+    subheadline: 'Für den Erhalt des Steigerwaldes',
+  },
+};
+
+export const NurText: Story = {
+  args: { banner: null, headline: 'Windwiderstand', subheadline: 'Bürgerinitiative Steigerwald' },
+};