use an env var for configurable proxy header (#8863)

src/state/queries/messages/accept-conversation.ts

@@ -1,9 +1,12 @@
-import {ChatBskyConvoAcceptConvo, ChatBskyConvoListConvos} from '@atproto/api'
+import {
+  type ChatBskyConvoAcceptConvo,
+  type ChatBskyConvoListConvos,
+} from '@atproto/api'
 import {useMutation, useQueryClient} from '@tanstack/react-query'
 
+import {DM_SERVICE_HEADERS} from '#/lib/constants'
 import {logger} from '#/logger'
 import {useAgent} from '#/state/session'
-import {DM_SERVICE_HEADERS} from './const'
 import {
   RQKEY as CONVO_LIST_KEY,
   RQKEY_ROOT as CONVO_LIST_ROOT_KEY,