feat(dashboard): add background agent live terminal peek and steer console (GOL-4)

[techoni3]

Summary

Introduces a live terminal peek and interactive steering console for background agents directly inside the Golem Dashboard, eliminating the need to leave the UI to run golem attach.

What changed

• Backend Terminal Peek Endpoint: Added GET /api/native-sessions/:sessionId/terminal?lines=N leveraging tmux capturePane to fetch real-time agent console scrollback.
• Backend Steer & Interrupt Endpoints: Added POST /api/native-sessions/:sessionId/message (delivering mid-turn steer or prompt briefs via deliverControlEnvelope) and POST /api/native-sessions/:sessionId/interrupt (sending C-c / interrupt signal).
• Native Session Drawer Tabs: Added Live Console & Steer and Activity & Events tabs to NativeSessionDrawer.
• Live Terminal Console: Monospace ANSI terminal viewport with live 2s auto-refresh, line length filters (50, 100, 250, 500), auto-scroll retention, copy attach command (golem attach <worker>), and copy output.
• Interactive Steer Composer: Docked message bar with send/steer button, quick prompt chips (status check, wrap up, interrupt), and delivery status toasts.
• Agent Card Shortcut: Added direct ›_ Peek console button on agent cards in /agents.
• Smoke Tests: Added dashboard/scripts/smoke-gol4-agent-peek.mjs and updated worker journey tests.

Test plan

• npm test passes cleanly (all 19 test suites passing).
• node dashboard/scripts/smoke-gol4-agent-peek.mjs passes cleanly.
• npm run dashboard:build builds production assets cleanly.

Notes for review

None.