style(stammbaum): widen side panel to 320px so longer names don't clip

The 268px width came from the spec mock; real names plus the
relationship pill ("Eugenie de Gruyter" + "Elternteil") need more
breathing room.

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

frontend/src/routes/stammbaum/+page.svelte

@@ -105,7 +105,7 @@ function zoomOut() {
 				/>
 			</div>
 			{#if selectedNode}
-				<aside class="w-[268px] shrink-0 overflow-y-auto border-l border-line bg-surface">
+				<aside class="w-[320px] shrink-0 overflow-y-auto border-l border-line bg-surface">
 					<StammbaumSidePanel
 						node={selectedNode}
 						canWrite={canWrite}