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

components/child/exercise-session.tsx

@@ -1,6 +1,7 @@
 "use client"
 
 import { useState, useCallback, useEffect, useRef } from "react"
+import { useRouter } from "next/navigation"
 import { motion, AnimatePresence } from "framer-motion"
 import { GatoMascota } from "@/components/child/gato-mascota"
 import NoChildError from "@/components/child/no-child-error"
@@ -20,7 +21,16 @@ interface Props {
   profile?: string
 }
 
+function profileHome(profile?: string) {
+  switch (profile?.toUpperCase()) {
+    case "FRANCESCA": return "/francesca"
+    case "SEBASTIAN": return "/sebastian"
+    default: return "/child"
+  }
+}
+
 export default function ExerciseSession({ topic, loadingMessage, completeMessage, profile }: Props) {
+  const router = useRouter()
   const [pageState, setPageState] = useState<PageState>("loading")
   const [exercise, setExercise] = useState<Exercise | null>(null)
   const [running, setRunning] = useState(true)
@@ -30,6 +40,21 @@ export default function ExerciseSession({ topic, loadingMessage, completeMessage
   const exerciseStartedAt = useRef<number>(Date.now())
   const startedAtRef = useRef(new Date().toISOString())
 
+  const backHref = profileHome(profile)
+
+  const BackBar = () => (
+    <button
+      onClick={() => {
+        stopSpeaking()
+        router.push(backHref)
+      }}
+      className="self-start flex items-center gap-2 bg-surface text-foreground border border-border rounded-xl px-4 py-2 text-base font-display font-semibold shadow-sm active:scale-95 transition-transform"
+    >
+      <span className="text-xl">←</span>
+      <span>Volver</span>
+    </button>
+  )
+
   const getChildId = useCallback(() => {
     const id = localStorage.getItem(CHILD_ID_KEY) || ""
     childIdRef.current = id
@@ -125,58 +150,74 @@ export default function ExerciseSession({ topic, loadingMessage, completeMessage
 
   if (pageState === "loading") {
     return (
-      <div className="flex-1 flex items-center justify-center">
-        <GatoMascota mood="coach" message={loadingMessage} size="sm" />
+      <div className="flex-1 flex flex-col p-4">
+        <BackBar />
+        <div className="flex-1 flex items-center justify-center">
+          <GatoMascota mood="coach" message={loadingMessage} size="sm" />
+        </div>
       </div>
     )
   }
 
   if (pageState === "error") {
-    return <NoChildError onRetry={resetSession} />
+    return (
+      <div className="flex-1 flex flex-col p-4">
+        <BackBar />
+        <div className="flex-1 flex items-center justify-center">
+          <NoChildError onRetry={resetSession} />
+        </div>
+      </div>
+    )
   }
 
   if (pageState === "complete") {
     return (
-      <div className="flex-1 flex flex-col items-center justify-center p-8 gap-6">
-        <GatoMascota mood="celebrate" message={completeMessage} size="lg" />
-        <p className="text-lg font-display">
-          Aciertos: {score}/{totalAttempts}
-        </p>
-        <button
-          onClick={resetSession}
-          className="bg-primary text-primary-foreground touch-target-lg rounded-2xl px-8 py-4 text-xl font-display font-bold"
-        >
-          Jugar de nuevo
-        </button>
+      <div className="flex-1 flex flex-col p-4">
+        <BackBar />
+        <div className="flex-1 flex flex-col items-center justify-center gap-6">
+          <GatoMascota mood="celebrate" message={completeMessage} size="lg" />
+          <p className="text-lg font-display">
+            Aciertos: {score}/{totalAttempts}
+          </p>
+          <button
+            onClick={resetSession}
+            className="bg-primary text-primary-foreground touch-target-lg rounded-2xl px-8 py-4 text-xl font-display font-bold"
+          >
+            Jugar de nuevo
+          </button>
+        </div>
       </div>
     )
   }
 
   return (
-    <div className="flex-1 flex flex-col items-center justify-center p-6 gap-6">
-      <TemporizadorVisual
-        durationMinutes={10}
-        onComplete={() => {
-          setRunning(false)
-          setPageState("complete")
-        }}
-        running={running}
-      />
+    <div className="flex-1 flex flex-col p-4 gap-4">
+      <BackBar />
+      <div className="flex-1 flex flex-col items-center justify-center gap-6">
+        <TemporizadorVisual
+          durationMinutes={10}
+          onComplete={() => {
+            setRunning(false)
+            setPageState("complete")
+          }}
+          running={running}
+        />
 
-      <AnimatePresence mode="wait">
-        <motion.div
-          key={exercise?.id || "empty"}
-          initial={{ opacity: 0, x: 50 }}
-          animate={{ opacity: 1, x: 0 }}
-          exit={{ opacity: 0, x: -50 }}
-          transition={{ duration: 0.25 }}
-          className="w-full max-w-md"
-        >
-          {exercise && (
-            <ExerciseDispatcher exercise={exercise} onComplete={handleComplete} />
-          )}
-        </motion.div>
-      </AnimatePresence>
+        <AnimatePresence mode="wait">
+          <motion.div
+            key={exercise?.id || "empty"}
+            initial={{ opacity: 0, x: 50 }}
+            animate={{ opacity: 1, x: 0 }}
+            exit={{ opacity: 0, x: -50 }}
+            transition={{ duration: 0.25 }}
+            className="w-full max-w-md"
+          >
+            {exercise && (
+              <ExerciseDispatcher exercise={exercise} onComplete={handleComplete} />
+            )}
+          </motion.div>
+        </AnimatePresence>
+      </div>
     </div>
   )
 }