Add an animated "agent is working" indicator so a silent gap (long-running
tool, the pause before the first token, sub-agent reasoning) reads as
"alive" rather than "hung": a braille spinner + phase label that runs on
its own timer, independent of the WebSocket event flow.

- New ActivityIndicator widget (rotating spinner + phase label, colored
  status_online), started/stopped from tui_app WS phase transitions
  (thinking / responding / planning / running <tool>) and stopped on
  stream_end/stopped/error and on connection drop.
- New StatusBar bottom line replaces Textual's Footer: indicator on the
  left, dim key-combo summary on the right. One line instead of the menu;
  the key bindings themselves stay on the App so the keys still work.
- Input box: TextArea min-height 3 -> 1, so the prompt is one line by
  default (auto-resize + max-height 12 unchanged).

Co-Authored-By: Claude <noreply@anthropic.com>

- Add right-side SessionsPanel widget (DataTable) listing server sessions.
- Wire SessionsPanel into TUI layout and session selection flow.
- Add SessionSelected / SessionListUpdated events and refresh logic.
- Implement /export slash command: markdown rendering + $EDITOR.
- Update /new, /sessions, /switch, /profile to use session_id/name/preview.
- Add integration tests for SessionsPanel and /export; update layout test.
- Update docs/navi_code_cli.md with new panel and command.

Co-Authored-By: Claude <noreply@anthropic.com>

- Add clients/terminal/tui package with micro-architecture:
  - events, context, chat_model, ws_bridge, permissions engine.
  - widgets: ChatPanel, StatusPanel, InputBox.
  - renderers: user/assistant messages, thinking, tool calls, errors,
    markdown, plain — registry-based and extensible.
  - slash commands: /help, /new, /sessions, /switch, /profile, /thinking,
    /compact, /quit — registry-based and extensible.
- Wire navi-code to launch TUI by default; keep click-CLI via --raw.
- Add textual>=0.70 dependency.
- Add TUI smoke tests via Textual Pilot.
- Add docs/plan_navi_code_tui.md with full Phase 4/5 roadmap.

Tests: 463 passed, 1 skipped (excluded unrelated websocket test).

Co-Authored-By: Claude <noreply@anthropic.com>