Dedupe double-fired rectificar-reminder toast on /mi-cursada

Student rectificar-reminder toast on /mi-cursada double-fires within 1s with inconsistent count text ('prácticas' plural then '1 práctica' singular on same page load) — cosmetic dedup, not a data/logic bug. Surfaced via applog spike triage 2026-07-18 (db-mars-cc). Repro: student f4e9354e, 23:00:07/23:00:08 UTC. Confirmed unrelated to MARS-507 #1 (different message/actor role — this is student-side, #1 is teacher-side lock nudge).