Restore the entity_authority alias the release path uses

Master moved the authority release parse into receipts.cpp and dropped the
route file's `authority` alias with it. The rebased release_named_bubble
still reads authority::Release and parse_abandon/parse_abdicate here.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017y4GeUXaw46fq2mDFGBVHN

Sunrise/src/server/bap/encrypted/activity_message/activity_message_route.cpp

@@ -47,6 +47,7 @@ namespace sunrise::server::bap::encrypted::activity_message {
 namespace {
 
 namespace service = middleware::bap::activity_message;
+namespace authority = middleware::bap::activity_message::entity_authority;
 namespace store = state::activity::receipts;
 namespace wire_schema = middleware::bap::activity_message::wire_schema;
 namespace communication = wire_schema::communication;