fix(ui): collapse retrieved subagent results

[xz-dev]

Summary

• collapse successful get_subagent_result output by default
• expand the unchanged full result with Pi's configured app.tools.expand keybinding (Ctrl-O by default)
• keep running and non-success results visible, and preserve the complete tool payload returned to the model

Testing

• npx vitest run test/status-note-wiring.test.ts
• npm run lint
• npm run typecheck
• npm run test
• npm run build