Add jefe mecánico to client booking flow

Cliente now picks a jefe mecánico after choosing the service so the
calendar shows that specific jefe's availability. Each jefe has its own
configurable parallel slot capacity (replacing the global SLOTS_PARALELOS
= 5). Admins manage jefes from /admin/jefes; jefes log in to /jefe to
see their daily agenda.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

prisma/schema.prisma

@@ -49,6 +49,7 @@ model Turno {
   clienteId      String
   autoId         String
   tipoServicioId String
+  jefeMecanicoId String
   fechaInicio    DateTime
   fechaFin       DateTime
   kilometros     Int
@@ -59,6 +60,19 @@ model Turno {
   cliente      Cliente      @relation(fields: [clienteId], references: [id])
   auto         Auto         @relation(fields: [autoId], references: [id])
   tipoServicio TipoServicio @relation(fields: [tipoServicioId], references: [id])
+  jefeMecanico JefeMecanico @relation(fields: [jefeMecanicoId], references: [id])
+}
+
+model JefeMecanico {
+  id             String   @id @default(cuid())
+  nombre         String
+  email          String   @unique
+  passwordHash   String
+  slotsParalelos Int      @default(1)
+  activo         Boolean  @default(true)
+  createdAt      DateTime @default(now())
+
+  turnos Turno[]
 }
 
 model HistorialServicio {