fix(studio): update WebMCP test for polyfill fallback

The "registers nothing when the browser has no WebMCP" test asserted
that document.modelContext was absent after mount. Since #3514 added
the @mcp-b/global polyfill fallback, the hook now installs
document.modelContext even when the browser has no native support —
that is the polyfill's job. The real assertion is that mounting does
not throw, which still holds.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: miga-heygen

packages/studio/src/webmcp/useStudioAgentTools.test.tsx

@@ -149,16 +149,16 @@ describe("useStudioAgentTools", () => {
     expect(signal?.aborted).toBe(true);
   });
 
-  it("registers nothing when the browser has no WebMCP", async () => {
+  it("boots cleanly when the browser has no native WebMCP", async () => {
     removeModelContext();
 
     await act(async () => {
       mountTools({ getSnapshot: () => snapshot() });
     });
 
-    // The assertion is that mounting did not throw; a browser without the API
-    // must still boot Studio.
-    expect(document).not.toHaveProperty("modelContext");
+    // The assertion is that mounting did not throw; a browser without the
+    // native API must still boot Studio. The polyfill may install
+    // document.modelContext as a fallback — that is expected.
   });
 
   it("registers nothing when the preference is turned off", async () => {