Show every agent tab's summary, not just the focused one

The tab bar's row-2 summary was painted only for the active tab. Add a
per-child summaryTextFor/summaryRawFor helper (active variants now
delegate to it), carry each tab's childID on its tabRect, and loop over
all visible tabs so each renders its own summary under its column.
Layout is unchanged (still 3 rows); narrow tabs clip as before.

Resolves the per-tab summary TODO item.

TODO.md

@@ -1 +0,0 @@
-- [ ] The per-tab agent summary text should display below the tab always, not just when the tab is focused.