style(web): use outline button for topbar CTA

Match the Sign In button styling from the hosted landing page —
border, rounded-lg, and accent hover background.

Author: dastratakos

packages/web/src/components/layout/topbar.tsx

@@ -1,5 +1,6 @@
 import { ExternalLink } from "lucide-react";
 import { ThemeToggle } from "@/components/layout/theme-toggle";
+import { Button } from "@/components/ui/button";
 import { useChapters } from "@/lib/use-chapters";
 
 export function Topbar({ runId }: { runId: string | null }) {
@@ -12,15 +13,12 @@ export function Topbar({ runId }: { runId: string | null }) {
 				{repoName && <span className="truncate font-medium text-foreground">{repoName}</span>}
 			</div>
 			<div className="flex shrink-0 items-center gap-2">
-				<a
-					href="https://stagereview.app"
-					target="_blank"
-					rel="noopener noreferrer"
-					className="flex items-center gap-1.5 text-muted-foreground text-sm transition-colors hover:text-foreground"
-				>
-					Try the full Stage experience
-					<ExternalLink className="size-3.5" />
-				</a>
+				<Button asChild variant="outline" size="sm">
+					<a href="https://stagereview.app" target="_blank" rel="noopener noreferrer">
+						Try the full Stage experience
+						<ExternalLink />
+					</a>
+				</Button>
 				<ThemeToggle />
 			</div>
 		</header>