ZoneOverview took its width from the Column it sits in, and a Column is as
wide as its widest child. The drawer's search widget supplies that; mission
control is the cards alone and has no search, so the only child left was the
loader — whose width came from the column, whose width came from the loader.
The cycle resolves to zero.
Full-height zero-width cards draw nothing, which is why multitasking was a
blurred backdrop and nothing else while every other signal read healthy:
zones 2, windows 1, subscribed true, loader active, item present, opacity 1,
progress 1. Bound to the panel's width instead, which is what this surface
covers anyway.
Also adds `overview missionControl` and `overview state` — the surface that
had been reported broken was the one nothing but a pill swipe could raise,
and the state readout is what located this.
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