Mark TUI, session list & dump, and transcription output epics as
completed — all child tasks done.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Defines Screen, Focus, AppState, SessionListItem with state transition
methods (new, enter_transcript, go_back). Reuses existing RawEntry and
AgentRef types. Includes 11 unit tests.
Closes claudbg-nq36
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>