Participant-change panel unreachable from the student surface (/mi-cursada/[id])

Surfaced by support ticket SOP-PLUTO-15 (practica e261d650-c9d2-4000-a350-461545e1731b): student created a practica, left asistente empty, reports "no me deja modificarlo". The capability EXISTS and she is authorised for it: PLUTO-544 shipped the 3-tier participant-change flow (d993009 v2.17.3). On /practicas/[id] she passes the participant gate (page.tsx:62-63,84) and viewerCanInitiate is true via user.id === practica.createdBy (page.tsx:229-232), so an empty asistente slot on an ungraded practica is Tier1 -> applies immediately (participant-change-actions.ts:63-65,78-85). The gap is purely the ENTRY POINT. /mi-cursada/[id]/page.tsx (180 lines) never imports or renders ParticipantChangePanel and has no link to /practicas/[id]; the panel is referenced only from /practicas/[id]/page.tsx:10,103,237. The student edit form also strips the operador/asistente block post-creation (practica-form.tsx:675) and the banner at :635 states participants cannot be changed - now FALSE for the creator, and that is the sentence she is reading. So a student can self-serve only by hand-typing /practicas/<uuid>, which no UI offers. NOT an authz bug - do not fix by relaxing any gate. Needs a UI decision: either render ParticipantChangePanel on /mi-cursada/[id] behind the same viewerCanInitiate computation, or link across to /practicas/[id] (check that surface is acceptable for a student viewer first). Also correct the stale practica-form.tsx:635 banner wording.