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>
Implements run_tui() with RAII terminal guard (TerminalGuard), panic hook
for safe cleanup, and 50ms poll event loop. Placeholder renderer draws a
bordered box. Wires into stubs.rs replacing the coming-soon stub.
Closes claudbg-ut9q
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>