Add minimal agent graph and stable input area

[areshand]

Summary

• render a minimal agent graph rooted at the orchestrator, with each direct agent's role, state, and current progress message
• restore the active › prompt after WebSocket status and orchestrator output redraws
• preserve partially typed follow-up text while asynchronous output arrives
• hide routine connection/count chrome and use a stable › input area
• document the interactive layout and add regression coverage for real TTY redraw behavior

Validation

• cd client && npm test (16 tests)
• bash tests/run.sh
• git diff --check