feat(cms/studio): agregar plantillas de curso reutilizables

- backend: CRUD básico de course templates y endpoint para crear curso desde plantilla
- migration: tabla course_templates con datos JSON del curso base
- frontend: nueva pantalla /course-templates para guardar y aplicar plantillas
- navegación: acceso desde menú Cursos

services/cms-service/migrations/20260406000010_course_templates.sql

@@ -0,0 +1,15 @@
+-- Course templates for reusable course blueprints
+CREATE TABLE IF NOT EXISTS course_templates (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    organization_id UUID NOT NULL REFERENCES organizations(id) ON DELETE CASCADE,
+    source_course_id UUID REFERENCES courses(id) ON DELETE SET NULL,
+    name TEXT NOT NULL,
+    description TEXT,
+    template_data JSONB NOT NULL,
+    created_by UUID REFERENCES users(id) ON DELETE SET NULL,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_course_templates_org_created
+    ON course_templates (organization_id, created_at DESC);