fix(web): place aria-selected on the role=tab element (#32) + assert it

Per WAI-ARIA, aria-selected must be on the same element carrying role="tab".
The previous impl placed it on an inner <span> via the render-prop, making it
invisible to assistive technology. Move both role="tab" and aria-selected to
the NavLink, compute currentKind once from useParams, drop the render-prop.
Add a Vitest assertion that the selected tab has aria-selected="true" and an
unselected tab has aria-selected="false".

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

web/src/authorities/authorities.test.tsx

@@ -36,6 +36,12 @@ test("kind tabs link to the other kinds", async () => {
   expect(await screen.findByRole("tab", { name: /place/i })).toHaveAttribute("href", "/authorities/place");
 });
 
+test("aria-selected is on the tab element and reflects the active kind", async () => {
+  renderApp(tree(), { route: "/authorities/person" });
+  expect(await screen.findByRole("tab", { name: /^person$/i })).toHaveAttribute("aria-selected", "true");
+  expect(screen.getByRole("tab", { name: /^place$/i })).toHaveAttribute("aria-selected", "false");
+});
+
 test("create without EN label shows required alert and does not POST", async () => {
   let posted = false;
   server.use(