An "Estimate" action asks the auto-routed auxiliary model for a rough token
count + complexity band (S/M/L) with a one-line rationale — tokens, not
dollars, since providers don't report cost reliably. POST /estimate (typed
title/body, for the create dialog) and POST /tasks/{id}/estimate (existing
cards) share one core. Desktop renders it inline ("~15k tok · Medium") with a
"makes a model call" disclaimer; SDK exports compactNumber.
