feat(renderer): surface MigrationPopup on the dashboard

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/renderer/routes/_shell.index.tsx

@@ -1,6 +1,12 @@
 import { createFileRoute } from "@tanstack/react-router";
+import { MigrationPopup } from "../components/MigrationPopup";
 import { SessionsBoard } from "../components/SessionsBoard";
 
 export const Route = createFileRoute("/_shell/")({
-	component: () => <SessionsBoard />,
+	component: () => (
+		<>
+			<MigrationPopup />
+			<SessionsBoard />
+		</>
+	),
 });