feat: live subagent dashboard widget in the TUI

Adds a widget above the editor (ctx.ui.setWidget) showing the research run
id, loop status, iteration, active agents with elapsed time, and recently
finished agents. Refreshed every 1.5s while work is running, hidden when
idle; timer is cleaned up on shutdown so reloads do not leak intervals.

CHANGELOG.md

@@ -31,6 +31,9 @@
   tree as paused, and resume requires the loop to actually be paused.
 - `read_artifact` now resolves symlinks before the confinement check, so a
   symlink inside the project cannot leak files from outside it.
+- Added a live subagent dashboard: a TUI widget above the editor shows the
+  research run id, loop status, iteration, active agents with elapsed time,
+  and recently finished agents (updated every 1.5 s, hidden when idle).
 
 ## 0.1.1 — 2026-07-31