fix(stammbaum): responsive /stammbaum layout — hidden md:block aside + fixed bottom sheet on mobile

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

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

@@ -102,13 +102,26 @@ function zoomOut() {
 				/>
 			</div>
 			{#if selectedNode}
-				<aside class="w-[320px] shrink-0 overflow-y-auto border-l border-line bg-surface">
+				<!-- Desktop: side panel on the right -->
+				<aside
+					class="hidden w-[320px] shrink-0 overflow-y-auto border-l border-line bg-surface md:block"
+				>
 					<StammbaumSidePanel
 						node={selectedNode}
 						canWrite={canWrite}
 						onClose={() => (selectedId = null)}
 					/>
 				</aside>
+				<!-- Mobile: fixed bottom sheet -->
+				<div
+					class="fixed inset-x-0 bottom-0 z-40 max-h-[60dvh] overflow-y-auto border-t border-line bg-surface shadow-lg md:hidden"
+				>
+					<StammbaumSidePanel
+						node={selectedNode}
+						canWrite={canWrite}
+						onClose={() => (selectedId = null)}
+					/>
+				</div>
 			{/if}
 		</div>
 	{/if}