feat: fase 5 — botones volver, seguridad APIs, infraestructura

- Botón 'Volver' en todas las sesiones de ejercicios (ExerciseSession)
- Botón 'Cambiar perfil' en las 3 home pages (Isabella/Francesca/Sebastián)
- Páginas inline de Isabella migradas a ExerciseSession (elimina código duplicado)
- APIs con try/catch: curriculum/next, dashboard/summary, fsrs/next, children
- Validación childId en curriculum/next (404 si no existe)
- /api/health endpoint para Docker healthcheck
- .env.example, .dockerignore, README.md creados
- docker-compose.yml con healthcheck en app service
- Test E2E: health endpoint + childId validation
- 62/62 tests pasan, TS exit 0

app/api/curriculum/next/route.ts

@@ -3,18 +3,27 @@ import { prisma } from "@/lib/db"
 import { getNextExercise } from "@/lib/curriculum/engine"
 
 export async function GET(request: NextRequest) {
-  const childId = request.nextUrl.searchParams.get("childId")
-  const topic = request.nextUrl.searchParams.get("topic") || "lectura"
-  if (!childId) {
-    return NextResponse.json({ error: "childId required" }, { status: 400 })
+  try {
+    const childId = request.nextUrl.searchParams.get("childId")
+    const topic = request.nextUrl.searchParams.get("topic") || "lectura"
+    if (!childId) {
+      return NextResponse.json({ error: "childId required" }, { status: 400 })
+    }
+
+    const child = await prisma.child.findUnique({
+      where: { id: childId },
+      select: { profile: true },
+    })
+
+    if (!child) {
+      return NextResponse.json({ error: "child not found" }, { status: 404 })
+    }
+
+    const profile = (request.nextUrl.searchParams.get("profile") || child.profile || "ISABELLA").toUpperCase()
+    const exercise = await getNextExercise(childId, topic, profile)
+    return NextResponse.json(exercise || { id: null, done: true })
+  } catch (error) {
+    console.error("[curriculum/next] error:", error)
+    return NextResponse.json({ error: "Internal error" }, { status: 500 })
   }
-
-  const child = await prisma.child.findUnique({
-    where: { id: childId },
-    select: { profile: true },
-  })
-
-  const profile = (request.nextUrl.searchParams.get("profile") || child?.profile || "ISABELLA").toUpperCase()
-  const exercise = await getNextExercise(childId, topic, profile)
-  return NextResponse.json(exercise || { id: null, done: true })
 }