feat: multi-profile system with Francesca and Sebastian curricula

- Add Profile enum (ISABELLA, FRANCESCA, SEBASTIAN) to Child model
- Add ?profile= query param override to /api/curriculum/next
- Pass profile prop from profile-specific pages to ExerciseSession
- Fix curriculum import paths (engine uses @/curriculum/ alias)
- Clear stale curriculumCache on dev reload
- Fix self-referential prerequisites in Francesca etapa-1
- Fix prerequisite chains in Francesca etapa-2,3,4 and Sebastian etapa-2,3
- Add Francesca curriculum: 2-3 digit sums, subtractions, multiplications, short readings
- Add Sebastian curriculum: 2-3 digit sums, interactive exercises, Argentine history, flags
- All 44 E2E tests pass, TypeScript compiles cleanly

prisma/schema.prisma

@@ -7,6 +7,12 @@ datasource db {
   url      = env("DATABASE_URL")
 }
 
+enum Profile {
+  ISABELLA
+  FRANCESCA
+  SEBASTIAN
+}
+
 model Parent {
   id           String    @id @default(cuid())
   email        String    @unique
@@ -75,6 +81,7 @@ model Family {
 model Child {
   id            String   @id @default(cuid())
   name          String?
+  profile       Profile  @default(ISABELLA)
   avatar        String?
   birthdate     DateTime?
   profileNotes  String?