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

curriculum/sebastian/etapa-3.ts

@@ -0,0 +1,39 @@
+import type { Stage } from '../types'
+
+const desafios = [
+  { a: 45, b: 67, res: 112 }, { a: 99, b: 88, res: 187 }, { a: 150, b: 250, res: 400 },
+  { a: 333, b: 444, res: 777 }, { a: 200, b: 555, res: 755 }, { a: 123, b: 321, res: 444 },
+]
+
+const exercises: any[] = []
+for (let i = 0; i < desafios.length; i++) {
+  const d = desafios[i]
+  exercises.push({
+    id: `seb3-desafio-${i}`,
+    stage: 3,
+    skillCode: `suma-challenge-${i}`,
+    type: 'eleccion',
+    prerequisites: i === 0 ? ['seb2-monedas'] : [`seb3-desafio-${i - 1}`],
+    content: {
+      instruction: `Desafío: ${d.a} + ${d.b}`,
+      audioText: `Sumá: ${d.a} más ${d.b}`,
+      emoji: '🏆',
+      options: [
+        { label: String(d.res), correct: true, id: String(d.res) },
+        { label: String(d.res + 10), correct: false, id: `c${i}a` },
+        { label: String(d.res - 5), correct: false, id: `c${i}b` },
+      ].sort(() => Math.random() - 0.5),
+    },
+    functionalContext: 'Desafío de sumas avanzadas. Utilizá descomposición.',
+    errorType: 'discriminacion-auditiva',
+  })
+}
+
+const stage: Stage = {
+  id: 3,
+  name: 'Desafíos de sumas',
+  description: 'Sumas 3 dígitos desafiantes con método Montessori.',
+  exercises,
+}
+
+export default stage