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

app/sebastian/historia/page.tsx

@@ -0,0 +1,12 @@
+import ExerciseSession from "@/components/child/exercise-session"
+
+export default function SebastianHistoria() {
+  return (
+    <ExerciseSession
+      topic="historia"
+      profile="SEBASTIAN"
+      loadingMessage="Preparando historia argentina..."
+      completeMessage="¡Terminaste historia por ahora!"
+    />
+  )
+}