fix(audit): corrige errores criticos y mayores, mejora UX/accesibilidad y optimiza rendimiento

- Arregla @require_auth, permisos, race conditions, locks de caja/stock
- Elimina N+1 en layaway, flotilla, dashboard y global_invoice
- Asegura folios atomicos para CFDI, ordenes de servicio y polizas
- Protege client_secret de MercadoLibre en backend
- Conecta botones/filtros de config, customers, accounting e invoicing
- Mejora accesibilidad (labels/aria-label) y estados de carga/vacio
- Limpia accounting.js obsoleto y consolida accounting.v9.js
- Actualiza cache busting a v32 y Service Worker a v32
- Documenta todo en docs/AUDIT_Y_MEJORAS_2026-06-15.md

Tests: 35 passed

pos/migrations/v4.10_fleet_permissions.sql

@@ -0,0 +1,20 @@
+-- v4.10: add fleet RBAC permissions for existing employees.
+-- Owner and admin get full fleet access; accountant and workshop get read access.
+
+INSERT INTO employee_permissions (employee_id, permission)
+SELECT e.id, p.perm
+FROM employees e
+CROSS JOIN (VALUES
+    ('fleet.view'),
+    ('fleet.create'),
+    ('fleet.edit'),
+    ('fleet.delete')
+) AS p(perm)
+WHERE e.role IN ('owner', 'admin')
+ON CONFLICT (employee_id, permission) DO NOTHING;
+
+INSERT INTO employee_permissions (employee_id, permission)
+SELECT e.id, 'fleet.view'
+FROM employees e
+WHERE e.role IN ('accountant', 'workshop')
+ON CONFLICT (employee_id, permission) DO NOTHING;