feat(dashboard): add UploadSuccessBanner component

Transient post-upload banner for issue #296: singular/plural German copy,
aria-live=polite for screen readers, manual X dismiss, 8s auto-dismiss.
"Jetzt ergänzen →" CTA links directly to /enrich so seniors can continue
straight into the enrichment flow after a batch upload.

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

frontend/src/lib/components/UploadSuccessBanner.svelte

@@ -0,0 +1,62 @@
+<script lang="ts">
+import * as m from '$lib/paraglide/messages.js';
+
+interface Props {
+	count: number;
+	onClose: () => void;
+}
+
+let { count, onClose }: Props = $props();
+
+const message = $derived(
+	count === 1 ? m.upload_banner_singular() : m.upload_banner_plural({ count })
+);
+
+$effect(() => {
+	const timer = setTimeout(onClose, 8000);
+	return () => clearTimeout(timer);
+});
+</script>
+
+<div
+	role="status"
+	aria-live="polite"
+	class="flex items-center gap-3 rounded-sm border border-line bg-accent-bg/60 px-4 py-3 text-ink"
+>
+	<svg
+		class="h-5 w-5 shrink-0 text-primary"
+		xmlns="http://www.w3.org/2000/svg"
+		fill="none"
+		viewBox="0 0 24 24"
+		stroke="currentColor"
+		stroke-width="2"
+		aria-hidden="true"
+	>
+		<path stroke-linecap="round" stroke-linejoin="round" d="M5 13l4 4L19 7" />
+	</svg>
+	<p class="flex-1 font-sans text-sm">
+		<span>{message}</span>
+		<a href="/enrich" class="ml-1 font-medium text-primary hover:underline">
+			{m.upload_banner_cta()}
+		</a>
+	</p>
+	<button
+		type="button"
+		data-testid="upload-banner-close"
+		aria-label={m.upload_banner_close()}
+		onclick={onClose}
+		class="inline-flex h-6 w-6 items-center justify-center rounded-sm text-ink-3 hover:bg-ink/10 hover:text-ink"
+	>
+		<svg
+			class="h-4 w-4"
+			xmlns="http://www.w3.org/2000/svg"
+			fill="none"
+			viewBox="0 0 24 24"
+			stroke="currentColor"
+			stroke-width="2"
+			aria-hidden="true"
+		>
+			<path stroke-linecap="round" stroke-linejoin="round" d="M6 18L18 6M6 6l12 12" />
+		</svg>
+	</button>
+</div>