feat: add Pro interface

hooks/use-is-embedded.ts

@@ -0,0 +1,17 @@
+"use client";
+
+import { createContext, useContext } from "react";
+
+/**
+ * True when the surrounding shell (currently only Pro) is rendering this
+ * page as a tab body rather than as the top-level route. Standard routes
+ * read this to hide their own NavigationRail and let the shell own the
+ * chrome.
+ *
+ * Provided via context by the Pro shell — no URL coupling, no iframe.
+ */
+export const EmbeddedContext = createContext<boolean>(false);
+
+export function useIsEmbedded(): boolean {
+  return useContext(EmbeddedContext);
+}