Widen or stop truncating toast feedbackKey so distinct validation messages don't collide

Toast feedbackKey generation truncates to ~26 chars, collapsing distinct validation messages into one key. Confirmed collision: 'no puede ser futura' and 'no puede ser anterior al <fecha>' both hash to toast:la-fecha-de-la-practica-no. Message text itself isn't stored, so post-hoc telemetry can't distinguish which validation fired -- a real coverage gap for future UX-pain triage on this route. Found investigating the 2026-08-09 uxpain digest (SOP-MARS-39 date-validation fix, bae9220) -- coder-mars-cc traced the collision while confirming no live wall exists.