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>

package.json

@@ -17,11 +17,17 @@
     "test": "vitest run",
     "test:watch": "vitest",
     "test:coverage": "vitest run --coverage",
-    "prepare": "svelte-kit sync || true"
+    "prepare": "svelte-kit sync || true",
+    "storybook": "storybook dev -p 6006",
+    "build-storybook": "storybook build"
   },
   "devDependencies": {
     "@iconify-json/lucide": "^1.2.114",
     "@iconify-json/mdi": "^1.2.3",
+    "@storybook/addon-a11y": "^10.5.0",
+    "@storybook/addon-docs": "^10.5.0",
+    "@storybook/addon-svelte-csf": "^5.1.2",
+    "@storybook/sveltekit": "^10.5.0",
     "@sveltejs/adapter-node": "^5.2.12",
     "@sveltejs/kit": "^2.65.0",
     "@sveltejs/vite-plugin-svelte": "^5.0.3",
@@ -31,7 +37,10 @@
     "@types/qrcode": "^1.5.6",
     "@types/sanitize-html": "^2.13.0",
     "@vitest/coverage-v8": "^2.1.9",
+    "msw": "^2.15.0",
+    "msw-storybook-addon": "^2.0.7",
     "openapi-typescript": "^7.4.0",
+    "storybook": "^10.5.0",
     "svelte": "^5.28.2",
     "svelte-check": "^4.1.4",
     "tailwindcss": "^4.1.18",
@@ -40,7 +49,6 @@
     "vitest": "^2.1.9"
   },
   "dependencies": {
-    "@fontsource-variable/aleo": "^5.2.7",
     "@fontsource-variable/lora": "^5.2.8",
     "@fontsource-variable/rubik": "^5.2.8",
     "@fontsource/inter": "^5.2.8",