Fix chat lobby persistence and identity save issues

[jolavillette]

Fix chat lobby persistence and identity save issues

This PR addresses a critical issue where private chat rooms and identity settings were not correctly persisted after restarting RetroShare

Changes

• Private Invitations: Added [setLobbyAutoSubscribe()] and [triggerConfigSave()] to [acceptLobbyInvite()]. This ensures private rooms are remembered and the UI can automatically reopen the tab on the next startup.
  • Note: These calls are placed outside the mDistributedChatMtx lock to avoid recursive deadlocks.
• Room Creation: Added [setLobbyAutoSubscribe()] to [createChatLobby()] for consistent persistence of user-created rooms.
• Identity Updates: Added [triggerConfigSave()] to [setIdentityForChatLobby()] so that changing your nickname/identity in a specific room is immediately saved to disk.

These modifications ensure that the AUTO_SUBSCRIBE flag is correctly set and flushed to chat.cfg, preventing the loss of private chat rooms upon application restart on macOS.