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/ImageModal.svelte

@@ -1,7 +1,6 @@
 <script lang="ts">
     import { onMount, onDestroy } from "svelte";
-    import Icon from "@iconify/svelte";
-    import "$lib/iconify-offline";
+    import IconButton from "$lib/components/IconButton.svelte";
 
     let {
         src,
@@ -33,12 +32,5 @@
         class="max-w-full max-h-full object-contain rounded shadow-2xl cursor-default"
         onclick={(e) => e.stopPropagation()}
     />
-    <button
-        type="button"
-        onclick={onclose}
-        class="absolute top-4 right-4 p-2 rounded-full bg-black/50 text-white hover:bg-black/70 transition-colors"
-        aria-label="Schließen"
-    >
-        <Icon icon="lucide:x" class="size-5" aria-hidden="true" />
-    </button>
+    <IconButton icon="lucide:x" label="Schließen" variant="ghost" size="md" onclick={onclose} class="absolute top-4 right-4" />
 </div>