Add regression tests for avatar reset and token-change refresh, stale 401 handling, idempotent session teardown and account-scoped preference cleanup. Update existing cubit tests for the new session dependency.
Refs: #1113
Use chat_id from the consultations payload for direct navigation and keep
the chat lookup as a fallback for legacy rows without chat_id.
- validate chat id in ChatRepository and make it nullable
- guard repeated taps while opening chat
- handle nullable chat id in ProfileCubit and EmptyChatScreen
related to #1106
