Mejoras de sesion: estabilizacion, IA, Nexus Yonke y marketplace B2B

- F0 blindaje: Redis/Celery, pg_hba sin trust LAN, secretos a env 600, backups, webhook auth, jobs muertos
- F1 caja: bugs POS, reembolsos al corte, apartados, CFDI, topes de descuento en cotizacion/apartado
- F2/F7 IA de catalogo: autocategorizacion, dedup de SKUs con embeddings, OCR de facturas, descripciones, claves SAT, limpieza de fitment
- F3 IA en el flujo: vision Yonke, preguntas MeLi, venta cruzada, anomalias, sinonimos, busqueda semantica (rerank/embeddings)
- F4/F8 escala y cartera: /metrics+Prometheus+Grafana, pool, score de credito, churn, metricas multi-tenant
- Nexus Yonke (M1-M6): modelo de datos 1-de-1, alta por donador, vitrina publica, MeLi usado, consignacion, garantia por dias, reportes, etiquetas
- Marketplace B2B entre yonkes (catalogo + pedidos cross-tenant)
- Seguridad: auth en /api/admin/* (35 endpoints), alertas por tenant
- Migraciones v4.27/v4.28; timers expire-demos y rollup-metrics

pos/services/billing.py

@@ -3,13 +3,21 @@
 from tenant_db import get_master_conn
 
 PLANS = {
+    # `demo` is a time-limited full trial (see scripts/expire_demos.py). It has
+    # no resource limits on purpose: a prospect must be able to import their
+    # real inventory without hitting a wall. Access is gated by the
+    # subscriptions.expires_at date, not by data volume.
+    'demo':       {'name': 'Demo',       'price_mxn': 0,    'max_products': None,  'max_employees': None, 'max_branches': None},
+    # Yonke: plan comercial para negocios de SOLO partes usadas (sin catálogo TecDoc)
+    'yonke':      {'name': 'Yonke',      'price_mxn': 299,  'max_products': None,  'max_employees': 10,   'max_branches': 1},
     'free':       {'name': 'Gratis',     'price_mxn': 0,    'max_products': 100,   'max_employees': 2,    'max_branches': 1},
     'basic':      {'name': 'Basico',     'price_mxn': 499,  'max_products': 5000,  'max_employees': 5,    'max_branches': 2},
+    'standard':   {'name': 'Estandar',   'price_mxn': 999,  'max_products': 20000, 'max_employees': 10,   'max_branches': 3},
     'pro':        {'name': 'Pro',        'price_mxn': 1499, 'max_products': 50000, 'max_employees': 15,   'max_branches': 5},
     'enterprise': {'name': 'Enterprise', 'price_mxn': 3999, 'max_products': None,  'max_employees': None, 'max_branches': None},
 }
 
-PLAN_ORDER = ['free', 'basic', 'pro', 'enterprise']
+PLAN_ORDER = ['free', 'demo', 'basic', 'standard', 'pro', 'enterprise']
 
 
 def get_plan(tenant_id):