Expect the default output entry to carry no name

- main stopped labelling the virtual default output with the first device's
  name (426acd22): a pinned sink is not re-routed, and which device the browser
  default resolves to is not knowable from here.
- The exploration still carried the older file, so this check passed locally
  and failed in CI, which tests the branch merged with main.
- AC8 is unchanged — Default is still a distinct entry beside the device it
  resolves to. Only the label it carries has moved.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/state/MediaDevices.test.ts

@@ -169,8 +169,10 @@ describe("MediaDevices selection", () => {
     const available = devices.audioOutput.available$.value;
     // Default follows the operating system and re-points when it changes, so
     // it is its own choice rather than an alias for the device it resolves to.
+    // It carries no name of its own precisely because which device it resolves
+    // to is not knowable from here.
     expect(available.get("spk1")).toEqual({ type: "name", name: "Speakers" });
-    expect(available.get("")).toEqual({ type: "default", name: "Speakers" });
+    expect(available.get("")).toEqual({ type: "default", name: null });
   });
 
   test("selecting one device kind leaves the others unchanged", () => {