Publish and unpublish on the local member

One way to put media on the session: publish(request) resolves with the local track once LiveKit has it, and unpublish(id) removes it. A request names a source with its device, processor and capture settings, so CaptureSettings on the client options goes, as do setMicrophoneEnabled and setCameraEnabled on the client and the four screen share fields on the local member; sharing is tracks$ having a screenShare track, and a capture failure rejects the promise. LocalMediaInputs becomes the list of initial requests, which also become the room defaults so that one permission prompt covers microphone and camera. The publisher keeps the requests across a reconnection and republishes what is not muted. The harness gains a Share screen button.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

sdk/README.md

@@ -30,8 +30,7 @@ const rtcClient = createMatrixRTCClient(
   client, // a matrix-js-sdk MatrixClient, logged in and syncing
   room, // the matrix-js-sdk Room, from client.getRoom() once the join has synced
   {
-    microphoneEnabled: true,
-    cameraEnabled: true,
+    publish: [{ source: "microphone" }, { source: "camera" }],
     audioOutputDeviceId$: constant(undefined),
   },
   {