feat(lotus): report the frame's audio outputs to the host (cinny #310)

Browsers hash deviceIds per frame/origin, so ids from the host's own
enumerateDevices() are unknown in here and select() fell back to the
default. io.lotus.audio_output_state now also carries
available: [{id,label}] (frame-valid ids), so the host's call-bar menu
can offer real choices.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017PCb59uY3UKqDqt7B6hzd5

src/lotus/lotusAudioOutput.test.ts

@@ -0,0 +1,24 @@
+/*
+Copyright 2026 Lotus Guild
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { expect, test } from "vitest";
+
+import { audioOutputList } from "./lotusAudioOutput";
+import { type AudioOutputDeviceLabel } from "../state/MediaDevices";
+
+test("audioOutputList labels every kind of output (cinny #310)", () => {
+  const m = new Map<string, AudioOutputDeviceLabel>([
+    ["", { type: "default", name: "Speakers" }],
+    ["a1", { type: "name", name: "Headset" }],
+    ["a2", { type: "number", number: 3 }],
+  ]);
+  expect(audioOutputList(m)).toEqual([
+    { id: "", label: "Default (Speakers)" },
+    { id: "a1", label: "Headset" },
+    { id: "a2", label: "Output 3" },
+  ]);
+});