feat(pwa): Toast-Store + Renderer

Toast-Queue als $state-Store mit Auto-Dismiss nach 3 s und manuellem
dismiss(id). Drei Kinds: info/error/success (Farbe). Renderer als
<Toast /> im Root-Layout, fix-positioniert oben mittig. Wird
vom Offline-Check der Schreib-Aktionen genutzt und später auch für
Sync-Abschluss-Meldungen.

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

src/lib/client/toast.svelte.ts

@@ -0,0 +1,25 @@
+export type ToastKind = 'info' | 'error' | 'success';
+export type Toast = { id: number; kind: ToastKind; message: string };
+
+class ToastStore {
+  toasts = $state<Toast[]>([]);
+  private nextId = 1;
+  private readonly dismissMs = 3000;
+
+  private push(kind: ToastKind, message: string): number {
+    const id = this.nextId++;
+    this.toasts = [...this.toasts, { id, kind, message }];
+    setTimeout(() => this.dismiss(id), this.dismissMs);
+    return id;
+  }
+
+  info(message: string): number { return this.push('info', message); }
+  error(message: string): number { return this.push('error', message); }
+  success(message: string): number { return this.push('success', message); }
+
+  dismiss(id: number): void {
+    this.toasts = this.toasts.filter((t) => t.id !== id);
+  }
+}
+
+export const toastStore = new ToastStore();

src/lib/components/Toast.svelte

@@ -0,0 +1,55 @@
+<script lang="ts">
+  import { X } from 'lucide-svelte';
+  import { toastStore } from '$lib/client/toast.svelte';
+</script>
+
+<div class="toasts" aria-live="polite" aria-atomic="true">
+  {#each toastStore.toasts as t (t.id)}
+    <div class="toast" class:error={t.kind === 'error'} class:success={t.kind === 'success'}>
+      <span class="msg">{t.message}</span>
+      <button class="close" aria-label="Schließen" onclick={() => toastStore.dismiss(t.id)}>
+        <X size={14} strokeWidth={2} />
+      </button>
+    </div>
+  {/each}
+</div>
+
+<style>
+  .toasts {
+    position: fixed;
+    top: 0.75rem;
+    left: 50%;
+    transform: translateX(-50%);
+    z-index: 200;
+    display: flex;
+    flex-direction: column;
+    gap: 0.35rem;
+    pointer-events: none;
+  }
+  .toast {
+    display: flex;
+    align-items: center;
+    gap: 0.6rem;
+    padding: 0.6rem 0.75rem;
+    background: #2b6a3d;
+    color: white;
+    border-radius: 10px;
+    font-size: 0.9rem;
+    pointer-events: auto;
+    box-shadow: 0 6px 18px rgba(0, 0, 0, 0.15);
+    max-width: min(92vw, 480px);
+  }
+  .toast.error { background: #c53030; }
+  .toast.success { background: #2b6a3d; }
+  .close {
+    background: transparent;
+    border: 0;
+    color: inherit;
+    cursor: pointer;
+    display: inline-flex;
+    align-items: center;
+    padding: 0.15rem;
+    opacity: 0.85;
+  }
+  .close:hover { opacity: 1; }
+</style>