Added timeline dialog (/timeline command or Cmd/Ctrl+T) for navigating, reverting, and forking from any point in the conversation (thanks to @aptdnfapt).
Added /undo and /redo commands for reverting and restoring messages in a session (thanks to @aptdnfapt).
Added fork button on user messages to create a new session from any point (thanks to @aptdnfapt).
Desktop app: keyboard shortcuts now use Cmd on macOS and Ctrl on web/other platforms (thanks to @sakhnyuk).
Migrated to OpenCode SDK v2 with improved API types and streaming.
