refactor(client): requireProfile() + asyncFetch wrapper

requireProfile():
- src/lib/client/profile.svelte.ts: neuer Helper, returnt das aktive
  Profile oder null nach standardisiertem alertAction
- 5x in recipes/[id]/+page.svelte: setRating, toggleFavorite, logCooked,
  addComment, toggleWishlist verlieren je 7 Zeilen Guard-Klausel
- profile-Variable im Closure macht den ! am profileStore.active obsolet

asyncFetch():
- src/lib/client/api-fetch-wrapper.ts: returnt Response auf 2xx, null
  nach alertAction auf Fehler
- 4 Call-Sites umgestellt: saveRecipe + saveTitle (recipes/[id]),
  saveEdit (admin/domains), rename (admin/profiles)
- admin/domains add() bewusst nicht migriert — inline-Error-UX statt Modal

Findings aus REVIEW-2026-04-18.md (Quick-Win 5) und redundancy.md

src/routes/admin/domains/+page.svelte

@@ -2,7 +2,8 @@
   import { onMount } from 'svelte';
   import { Pencil, Check, X, Globe } from 'lucide-svelte';
   import type { AllowedDomain } from '$lib/types';
-  import { confirmAction, alertAction } from '$lib/client/confirm.svelte';
+  import { confirmAction } from '$lib/client/confirm.svelte';
+  import { asyncFetch } from '$lib/client/api-fetch-wrapper';
   import { requireOnline } from '$lib/client/require-online';
 
   let domains = $state<AllowedDomain[]>([]);
@@ -64,22 +65,19 @@
     if (!requireOnline('Das Speichern')) return;
     saving = true;
     try {
-      const res = await fetch(`/api/domains/${d.id}`, {
-        method: 'PATCH',
-        headers: { 'content-type': 'application/json' },
-        body: JSON.stringify({
-          domain: editDomain.trim(),
-          display_name: editLabel.trim() || null
-        })
-      });
-      if (!res.ok) {
-        const body = await res.json().catch(() => ({}));
-        await alertAction({
-          title: 'Speichern fehlgeschlagen',
-          message: body.message ?? `HTTP ${res.status}`
-        });
-        return;
-      }
+      const res = await asyncFetch(
+        `/api/domains/${d.id}`,
+        {
+          method: 'PATCH',
+          headers: { 'content-type': 'application/json' },
+          body: JSON.stringify({
+            domain: editDomain.trim(),
+            display_name: editLabel.trim() || null
+          })
+        },
+        'Speichern fehlgeschlagen'
+      );
+      if (!res) return;
       cancelEdit();
       await load();
     } finally {