refactor(stammbaum): extract RelationshipChip and AddRelationshipForm

Split StammbaumCard from 366 to 196 lines by extracting:
- RelationshipChip.svelte — single relationship list item with optional delete
- AddRelationshipForm.svelte — self-contained add-relationship form with open/close state

Both components have browser-mode spec tests covering rendering and interaction.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/components/RelationshipChip.svelte

@@ -0,0 +1,49 @@
+<script lang="ts">
+import { enhance } from '$app/forms';
+import { m } from '$lib/paraglide/messages.js';
+
+interface Props {
+	chipLabel: string;
+	otherName: string;
+	yearRange?: string;
+	canWrite: boolean;
+	relId: string;
+}
+
+let { chipLabel, otherName, yearRange = '', canWrite, relId }: Props = $props();
+</script>
+
+<li class="flex items-center gap-2 py-2">
+	<span
+		class="inline-flex shrink-0 items-center rounded-full border border-accent/40 bg-accent/15 px-2 py-0.5 font-sans text-xs font-bold tracking-widest text-ink uppercase"
+	>
+		{chipLabel}
+	</span>
+	<span class="min-w-0 flex-1 truncate font-serif text-sm text-ink">
+		{otherName}
+	</span>
+	{#if yearRange}
+		<span class="shrink-0 font-sans text-xs text-ink-3" data-testid="year-range">{yearRange}</span>
+	{/if}
+	{#if canWrite}
+		<form method="POST" action="?/deleteRelationship" use:enhance class="shrink-0">
+			<input type="hidden" name="relId" value={relId} />
+			<button
+				type="submit"
+				aria-label="{m.btn_delete()} — {otherName}"
+				class="inline-flex h-8 w-8 items-center justify-center text-ink-3 transition-colors hover:text-red-600"
+			>
+				<svg
+					class="h-3.5 w-3.5"
+					viewBox="0 0 24 24"
+					fill="none"
+					stroke="currentColor"
+					stroke-width="2"
+					aria-hidden="true"
+				>
+					<path stroke-linecap="round" stroke-linejoin="round" d="M6 18L18 6M6 6l12 12" />
+				</svg>
+			</button>
+		</form>
+	{/if}
+</li>