@all is a broadcast to all workspace members — it should not trigger
the assignee agent's on_comment. Previously @all was treated as
"includes everyone" and allowed the trigger.
Changes:
- commentMentionsOthersButNotAssignee now checks HasMentionAll() early
and returns true (suppress) when @all is present
- Fix authRequestWithAgent test helper that was making a duplicate HTTP
request (one as member, one as agent)
Tests: 5 new @all unit test cases, 2 new @all integration test cases.