feat: Implement external MySQL integration for LMS enrollments and grade synchronization, including external_id and tipo_nota support.

services/lms-service/migrations/20260226040000_add_external_id_to_enrollments.sql

@@ -0,0 +1,2 @@
+-- Add external_id to enrollments to map idDetalleContrato from the external system
+ALTER TABLE enrollments ADD COLUMN IF NOT EXISTS external_id INTEGER;