feat: QR-Code, vCard-Export, Org-Gruppenansicht im Adressbuch

- vcard.ts: shared vCard-Generator (downloadVCard, downloadVCardAll, buildVCardString)
- QrModal.svelte + QrButton.svelte: wiederverwendbare QR-Komponenten mit PNG-Download
- AdressbuchBlock: Org-Gruppenansicht (Toggle), QR + vCard pro Kontakt,
  Buchstaben-Trennzeilen, Such-Highlight, "Alle exportieren", Print-Styles
- ContactCard: vCard-Download-Button
- PostActions: QR-Button für Seiten-URL
- qrcode npm-Paket hinzugefügt

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/lib/components/PostActions.svelte

@@ -3,6 +3,7 @@
   import "$lib/iconify-offline";
   import { env } from "$env/dynamic/public";
   import { useTranslate, T } from "$lib/translations";
+  import QrButton from "$lib/components/QrButton.svelte";
 
   let {
     url,
@@ -194,6 +195,12 @@
     >
       <Icon icon="mdi:printer-outline" class="size-3.5" />
     </button>
+    <QrButton
+      value={url}
+      label={title}
+      sublabel="Link teilen"
+      class="inline-flex items-center px-2.5 py-1 text-base text-stein-600 hover:bg-stein-50 hover:text-stein-900 transition-colors"
+    />
   </div>
 
   {#if readingTimeMinutes != null && readingTimeMinutes > 0}