feat: fase 2+3 — expansion masiva multi-perfil + bug fixes + hardening

Fase 2 (expansion):
- Francesca: +6 etapas matematicas (5-10), +7 etapas lectura (3-9), +2 ortografia
- Sebastian: +8 etapas matematicas (4-11), +6 lectura, +3 historia, +3 geografia, +1 banderas
- Nuevas paginas: ortografia, lectura, geografia, matematicas
- ~900 ejercicios nuevos, paridad ~500 por perfil

Fase 3 (bug fixes + hardening):
- Fix: SessionLog auto-create en grade route
- Fix: engine cache (no borrar antes de revisar)
- Fix: FSRS cards actualizadas en flujo curriculum
- Fix: responseMs real (no hardcodeado 3000)
- Fix: options dentro de content en sebastian etapa-1
- Fix: trazo-letra consonantes crash
- Security: execFileSync anti-command-injection en TTS
- DB: 18 cascade deletes + indices + unique constraints
- APIs debug: reset, state, seed
- Docker: espeak-ng + prisma + user/group
- E2E: 23 tests nuevos (curriculum-flow.spec.ts)
- Code review: tailwind colors, middleware dev mode, eslint config

Verificado: tsc exit 0, build exit 0, 61 E2E tests pass

components/child/exercise-session.tsx

@@ -27,6 +27,7 @@ export default function ExerciseSession({ topic, loadingMessage, completeMessage
   const [score, setScore] = useState(0)
   const [totalAttempts, setTotalAttempts] = useState(0)
   const childIdRef = useRef<string>("")
+  const exerciseStartedAt = useRef<number>(Date.now())
   const startedAtRef = useRef(new Date().toISOString())
 
   const getChildId = useCallback(() => {
@@ -52,6 +53,7 @@ export default function ExerciseSession({ topic, loadingMessage, completeMessage
         return null
       }
       setExercise(data)
+      exerciseStartedAt.current = Date.now()
       setPageState("ready")
       return data
     } catch {
@@ -76,6 +78,7 @@ export default function ExerciseSession({ topic, loadingMessage, completeMessage
       : null
 
     try {
+      const responseMs = Date.now() - exerciseStartedAt.current
       await fetch("/api/curriculum/grade", {
         method: "POST",
         headers: { "Content-Type": "application/json" },
@@ -85,7 +88,7 @@ export default function ExerciseSession({ topic, loadingMessage, completeMessage
           skillCode: ex.skillCode,
           correct,
           promptLevel: 0,
-          responseMs: 3000,
+          responseMs,
           errorType,
           stage: ex.stage,
         }),