feat(geschichten): add stripHtml util and GeschichtenCard component

stripHtml() strips tags via DOMParser (browser) with a regex fallback for
SSR. plainExcerpt() truncates at a word boundary with an ellipsis. Both
covered by Vitest specs.

GeschichtenCard renders the top 3 published stories about a person on
/persons/[id], with an editorial excerpt, publication date, author, and a
"+ Geschichte schreiben" link visible only to BLOG_WRITERs. Footer link to
/geschichten?personId=... appears once geschichten.length >= 3.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/lib/components/GeschichtenCard.svelte

@@ -0,0 +1,87 @@
+<script lang="ts">
+import { m } from '$lib/paraglide/messages.js';
+import type { components } from '$lib/generated/api';
+import { plainExcerpt } from '$lib/utils/stripHtml';
+import { formatDate } from '$lib/utils/date';
+
+type Geschichte = components['schemas']['Geschichte'];
+
+interface Props {
+	geschichten: Geschichte[];
+	personId: string;
+	personName: string;
+	canWrite: boolean;
+}
+
+let { geschichten, personId, personName, canWrite }: Props = $props();
+
+const visible = $derived(geschichten.slice(0, 3));
+const hasOverflow = $derived(geschichten.length >= 3);
+
+function formatPublishedDate(g: Geschichte): string | null {
+	if (!g.publishedAt) return null;
+	return formatDate(g.publishedAt.slice(0, 10), 'short');
+}
+
+function authorName(g: Geschichte): string {
+	const a = g.author;
+	if (!a) return '';
+	const full = [a.firstName, a.lastName].filter(Boolean).join(' ').trim();
+	return full || a.email || '';
+}
+</script>
+
+{#if geschichten.length > 0}
+	<section
+		aria-labelledby="geschichten-card-heading"
+		class="rounded-sm border border-line bg-surface p-6 shadow-sm"
+	>
+		<header class="mb-5 flex items-center justify-between">
+			<h2
+				id="geschichten-card-heading"
+				class="font-sans text-xs font-bold tracking-widest text-ink-3 uppercase"
+			>
+				{m.geschichten_card_heading()}
+			</h2>
+			{#if canWrite}
+				<a
+					href="/geschichten/new?personId={personId}"
+					class="inline-flex items-center font-sans text-sm font-medium text-ink/60 hover:text-ink"
+				>
+					{m.geschichten_card_write_action()}
+				</a>
+			{/if}
+		</header>
+
+		<ul class="flex flex-col gap-4">
+			{#each visible as g (g.id)}
+				<li class="flex flex-col gap-1 border-b border-line pb-3 last:border-0 last:pb-0">
+					<a
+						href="/geschichten/{g.id}"
+						class="font-serif text-base font-bold text-ink hover:underline"
+					>
+						{g.title}
+					</a>
+					<p class="font-sans text-xs text-ink-3">
+						{authorName(g)}
+						{#if formatPublishedDate(g)}· {formatPublishedDate(g)}{/if}
+					</p>
+					{#if g.body}
+						<p class="font-serif text-sm text-ink-2">{plainExcerpt(g.body, 80)}</p>
+					{/if}
+				</li>
+			{/each}
+		</ul>
+
+		{#if hasOverflow}
+			<footer class="mt-4 border-t border-line pt-3">
+				<a
+					href="/geschichten?personId={personId}"
+					class="inline-flex items-center font-sans text-sm font-medium text-ink hover:underline"
+				>
+					{m.geschichten_card_show_all_for_person({ name: personName })} →
+				</a>
+			</footer>
+		{/if}
+	</section>
+{/if}