feat(ui): custom dialog replaces all remaining window.alert() calls

alertAction({title, message}) returns Promise<void> and renders the
same ConfirmDialog with infoOnly:true — single OK button, no Abbrechen.
Replaces:
- 'Bitte Profil wählen.' (recipe rating / favorite / cooked / comment)
- 'Bitte Profil wählen, um zu liken.' (wishlist)
- 'Profil konnte nicht angelegt werden' (ProfileSwitcher)
- 'Umbenennen fehlgeschlagen' (admin/profiles)
- 'Speichern fehlgeschlagen' (preview)

No window.alert() or window.confirm() left in the codebase.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/routes/preview/+page.svelte

@@ -2,6 +2,7 @@
   import { page } from '$app/stores';
   import { goto } from '$app/navigation';
   import RecipeView from '$lib/components/RecipeView.svelte';
+  import { alertAction } from '$lib/client/confirm.svelte';
   import type { Recipe } from '$lib/types';
 
   let targetUrl = $state(($page.url.searchParams.get('url') ?? '').trim());
@@ -45,7 +46,10 @@
     saving = false;
     if (!res.ok) {
       const body = await res.json().catch(() => ({}));
-      alert(`Speichern fehlgeschlagen: ${body.message ?? res.status}`);
+      await alertAction({
+        title: 'Speichern fehlgeschlagen',
+        message: body.message ?? `HTTP ${res.status}`
+      });
       return;
     }
     const body = await res.json();