migrate the join link and join request queries to the chat client

The logged-out join link preview path built an ad-hoc AtpAgent pointed at
CHAT_SERVICE. It is now a module-level unauthenticated lex client against
the same service, so the client is built once rather than per call.

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

src/state/queries/messages/list-join-requests.ts

@@ -2,10 +2,10 @@ import {useEffect} from 'react'
 import {ChatBskyConvoDefs} from '@atproto/api'
 import {useInfiniteQuery, useQueryClient} from '@tanstack/react-query'
 
-import {DM_SERVICE_HEADERS} from '#/lib/constants'
 import {useMessagesEventBus} from '#/state/messages/events'
 import {createQueryKey} from '#/state/queries/util'
-import {useAgent} from '#/state/session'
+import {useChatClient} from '#/state/session'
+import {chat} from '#/lexicons'
 import {STALE} from '..'
 
 export const JOIN_REQUESTS_THRESHOLD = 20
@@ -22,7 +22,7 @@ export function useListJoinRequestsQuery({
   convoId: string | undefined
   enabled?: boolean
 }) {
-  const agent = useAgent()
+  const client = useChatClient()
   const queryClient = useQueryClient()
   const messagesBus = useMessagesEventBus()
   const isEnabled = enabled !== false && !!convoId
@@ -54,11 +54,12 @@ export function useListJoinRequestsQuery({
     enabled: isEnabled,
     queryKey: createListJoinRequestsQueryKey({convoId: convoId ?? ''}),
     queryFn: async ({pageParam}) => {
-      const {data} = await agent.chat.bsky.group.listJoinRequests(
-        {convoId: convoId!, cursor: pageParam, limit: JOIN_REQUESTS_THRESHOLD},
-        {headers: DM_SERVICE_HEADERS},
-      )
-      return data
+      return await client.call(chat.bsky.group.listJoinRequests, {
+        // guarded by `isEnabled`
+        convoId: convoId!,
+        cursor: pageParam,
+        limit: JOIN_REQUESTS_THRESHOLD,
+      })
     },
     initialPageParam: undefined as string | undefined,
     getNextPageParam: page => page.cursor,