Clean up dead additive totalPracticas computation in getStudentProfileSummary

getStudentProfileSummary (src/lib/queries.ts:2769) computes an ADDITIVE operatorCount+assistantCount totalPracticas — venus's known double-count failure pattern (venus KPI-semantics cross-check, 2026-07-13). Currently dead code: every consumer renders comoOperador/comoAsistente separately, this summed field is never rendered. Currently safe only because createPractica rejects operadorId===asistenteId at the app layer (practica-actions.ts:107), an app-level guard not a DB CHECK constraint - landmine if the field is ever wired into a UI without the same guard, or the guard is bypassed. Fix: delete the dead computation, or replace with the same DISTINCT-practicaId CTE used elsewhere (getStudentKpis, fn_getInformesBundle). Pluto has no separate participacion table (role is a column on practica, not a join row) so Pluto structurally avoids venus's divergent-count bug everywhere except this one dead field.