Fix delete/get/list_dispatch: keyword auth_header + ClientResp .data unwrap

[trialize]

Problem

AgentDispatchServiceClient#delete_dispatch, #get_dispatch, and #list_dispatch are unusable as shipped:

1. Positional grant → ArgumentError. All three pass the grant positionally to AuthMixin#auth_header, which only accepts the video_grant: keyword:

   headers: auth_header(VideoGrant.new(roomAdmin: true, room: room_name))

   Every call raises ArgumentError: wrong number of arguments (given 1, expected 0) from auth_mixin.rb before any request is sent. #create_dispatch is the only method that passes the keyword correctly.

2. res.agent_dispatches off a ClientResp. #get_dispatch / #list_dispatch read res.agent_dispatches directly off the Twirp::ClientResp returned by rpc, instead of res.data.agent_dispatches — a NoMethodError that the first bug masked.

Fix

Minimal: pass video_grant: and unwrap res.data in the three methods. #create_dispatch is unchanged.

Verification

Against a live LiveKit server: create_dispatch → list_dispatch (shows the dispatch) → delete_dispatch → list_dispatch (gone), all returning cleanly. Before the fix each of the three raised ArgumentError from auth_mixin.rb.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}