refactor(consolidate): IconButton + Badge-solid + @layer base + Massen-Migration

E: app.css Base-h1–h6 in @layer base → text-*!-Hacks in Titeln entfernt.
Neue Atoms: IconButton (runde Icon-Buttons), Badge solid-Variante + uppercase.

Migrationen (6 parallele Pässe):
- IconButton: 19 runde Nav/Close-Buttons (Carousel, Galleries, QuoteCarousel,
  PostOverview, Organisations, ImageModal).
- Badge: Kategorie/Status-Pills (PostCard, BlogOverview, kalender, Comments,
  CalendarBlock, FilesBlock, SearchableText, Stellingnahme).
- ui-Atome: Formular-Inputs (Comments, termin-melden, Stellingnahme) → TextInput/
  Textarea/Checkbox/SearchField; dunkle NewsletterInline bewusst raw.
- Button-Atom: ~20 inline Buttons in StellingnahmeGeneratorBlock.
- Radius-Sweep: Cards→rounded-lg (viele via .card-surface), Buttons/Inputs→rounded-md,
  Chips→rounded-full; StrommixBlock/Calendar/Files/Adressbuch u.a.

svelte-check 0 errors, voller Prod-Build grün.

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

src/lib/components/blocks/OrganisationsBlock.svelte

@@ -12,6 +12,7 @@
   import SectionHeader from "$lib/components/SectionHeader.svelte";
   import SectionGrid from "$lib/components/SectionGrid.svelte";
   import InfoCard from "$lib/components/InfoCard.svelte";
+  import IconButton from "$lib/components/IconButton.svelte";
 
   function organisationLogoField(o: OrganisationEntry) {
     return extractCmsImageField(o.logo);
@@ -235,22 +236,8 @@
         {/each}
       </div>
       {#if orgs.length > 2}
-        <button
-          type="button"
-          onclick={() => scrollByPage(-1)}
-          aria-label="Vorherige Organisationen"
-          class="hidden md:flex absolute -left-3 top-1/2 -translate-y-1/2 -translate-x-1/2 size-7 items-center justify-center rounded-full bg-white border border-stein-200 shadow-md hover:bg-stein-50 transition"
-        >
-          <Icon icon="lucide:chevron-left" class="size-4" aria-hidden="true" />
-        </button>
-        <button
-          type="button"
-          onclick={() => scrollByPage(1)}
-          aria-label="Weitere Organisationen"
-          class="hidden md:flex absolute -right-3 top-1/2 -translate-y-1/2 translate-x-1/2 size-7 items-center justify-center rounded-full bg-white border border-stein-200 shadow-md hover:bg-stein-50 transition"
-        >
-          <Icon icon="lucide:chevron-right" class="size-4" aria-hidden="true" />
-        </button>
+        <IconButton icon="lucide:chevron-left" label="Vorherige Organisationen" variant="surface" size="sm" onclick={() => scrollByPage(-1)} class="hidden md:flex absolute -left-3 top-1/2 -translate-y-1/2 -translate-x-1/2" />
+        <IconButton icon="lucide:chevron-right" label="Weitere Organisationen" variant="surface" size="sm" onclick={() => scrollByPage(1)} class="hidden md:flex absolute -right-3 top-1/2 -translate-y-1/2 translate-x-1/2" />
       {/if}
     </div>
     {#if showAddOrganisationCard}