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

prisma/schema.prisma

@@ -23,7 +23,7 @@ model Parent {
   updatedAt    DateTime  @updatedAt
 
   familyId String?
-  family   Family? @relation(fields: [familyId], references: [id])
+  family   Family? @relation(fields: [familyId], references: [id], onDelete: Cascade)
 
   sessions Session[]
   accounts Account[]
@@ -34,7 +34,7 @@ model Session {
   email        String?
   userId       String?
   parentId     String?
-  parent       Parent?  @relation(fields: [parentId], references: [id])
+  parent       Parent?  @relation(fields: [parentId], references: [id], onDelete: Cascade)
   token        String   @unique
   expiresAt    DateTime
   ipAddress    String?
@@ -48,7 +48,7 @@ model Account {
   accountId       String
   providerId      String
   userId          String
-  user            Parent  @relation(fields: [userId], references: [id])
+  user            Parent  @relation(fields: [userId], references: [id], onDelete: Cascade)
   accessToken     String?
   refreshToken    String?
   idToken         String?
@@ -74,8 +74,8 @@ model Family {
   createdAt DateTime @default(now())
   updatedAt DateTime @updatedAt
 
-  parents  Parent[]
-  children Child[]
+  parents  Parent[] @relation(onDelete: Cascade)
+  children Child[]  @relation(onDelete: Cascade)
 }
 
 model Child {
@@ -89,13 +89,13 @@ model Child {
   updatedAt     DateTime @updatedAt
 
   familyId String
-  family   Family @relation(fields: [familyId], references: [id])
+  family   Family @relation(fields: [familyId], references: [id], onDelete: Cascade)
 
-  devices     Device[]
-  sessions    SessionLog[]
-  fsrsCards   FsrsCard[]
-  milestones  Milestone[]
-  curriculumProgress CurriculumProgress[]
+  devices     Device[]              @relation(onDelete: Cascade)
+  sessions    SessionLog[]          @relation(onDelete: Cascade)
+  fsrsCards   FsrsCard[]            @relation(onDelete: Cascade)
+  milestones  Milestone[]           @relation(onDelete: Cascade)
+  curriculumProgress CurriculumProgress[] @relation(onDelete: Cascade)
 }
 
 model Device {
@@ -107,7 +107,10 @@ model Device {
   createdAt         DateTime @default(now())
 
   childId String
-  child   Child @relation(fields: [childId], references: [id])
+  child   Child @relation(fields: [childId], references: [id], onDelete: Cascade)
+
+  @@index([childId])
+  @@index([deviceFingerprint])
 }
 
 model SessionLog {
@@ -118,9 +121,11 @@ model SessionLog {
   skillsPracticed String?
 
   childId String
-  child   Child @relation(fields: [childId], references: [id])
+  child   Child @relation(fields: [childId], references: [id], onDelete: Cascade)
 
-  skillAttempts SkillAttempt[]
+  skillAttempts SkillAttempt[] @relation(onDelete: Cascade)
+
+  @@index([childId])
 }
 
 model SkillAttempt {
@@ -135,7 +140,10 @@ model SkillAttempt {
   createdAt   DateTime @default(now())
 
   sessionLogId String
-  sessionLog   SessionLog @relation(fields: [sessionLogId], references: [id])
+  sessionLog   SessionLog @relation(fields: [sessionLogId], references: [id], onDelete: Cascade)
+
+  @@index([sessionLogId])
+  @@index([skillCode])
 }
 
 model CurriculumProgress {
@@ -146,9 +154,10 @@ model CurriculumProgress {
   completedAt DateTime?
 
   childId String
-  child   Child @relation(fields: [childId], references: [id])
+  child   Child @relation(fields: [childId], references: [id], onDelete: Cascade)
 
   @@unique([childId, topic, stage])
+  @@index([childId])
 }
 
 model FsrsCard {
@@ -163,7 +172,10 @@ model FsrsCard {
   updatedAt  DateTime @updatedAt
 
   childId String
-  child   Child @relation(fields: [childId], references: [id])
+  child   Child @relation(fields: [childId], references: [id], onDelete: Cascade)
+
+  @@unique([childId, skillCode])
+  @@index([childId])
 }
 
 model Milestone {
@@ -172,9 +184,10 @@ model Milestone {
   reachedAt DateTime @default(now())
 
   childId String
-  child   Child @relation(fields: [childId], references: [id])
+  child   Child @relation(fields: [childId], references: [id], onDelete: Cascade)
 
   @@unique([childId, skillCode])
+  @@index([childId])
 }
 
 model PendingPairing {
@@ -184,4 +197,6 @@ model PendingPairing {
   childId           String?
   createdAt         DateTime @default(now())
   expiresAt         DateTime
+
+  @@index([expiresAt])
 }