test(web): find the sidebar Today button by its English label

The shell contrast test added on main looks up the sidebar button by the
old German source text, which this branch replaces with "Today".

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MRtGG9ARfqqhma3t85Ro2u

apps/web/e2e/chat-contrast.spec.ts

@@ -221,8 +221,8 @@ test("shell surfaces stay readable in light and dark themes", async ({ page }, t
       inside: true,
     });
     await expectReadable(
-      sidebar.getByRole("button", { name: "Heute", exact: true }),
-      `${theme}: Heute`,
+      sidebar.getByRole("button", { name: "Today", exact: true }),
+      `${theme}: Today`,
       { inside: true },
     );
     await expectReadable(