Other users with `course:manage` can add lessons to the products they don't own

[rajat1saxena]

Because createLesson checks only the global permission string, not course ownership.

In apps/web/graphql/lessons/logic.ts, the flow is:

1. Authenticate user.
2. Require course:manage.
3. Fetch course by courseId and domain.
4. Create lesson and push it into that course.

The missing check is between steps 3 and 4. It should call the existing owner-aware helper, like:

if (!canManageCourseInContext(course, ctx)) {
    throw new Error(responses.action_not_allowed);
}

That helper already encodes the intended rule in apps/web/graphql/courses/permissions.ts: course:manage_any can manage any course, while course:manage can manage only owned courses.

So the root cause is: createLesson treats course:manage as tenant-wide course management. Also, the public API lesson creation route delegates to the same function at apps/web/app/api/products/[productId]/lessons/route.ts, so fixing createLesson should close both GraphQL and REST creation paths.