Delete web package

Soft-delete a web package.

Returns 409 when a lesson in a live course still references the package — deleting it would leave that lesson with no content. Otherwise the package is soft-deleted and 204 is returned.

By-id rather than a batch envelope: the conflict outcome has no natural home in a per-row batch result, and batch-responses.md warns specifically against letting a ConflictError fall through the document-level path mid-batch. Matches DELETE /v2/students/{id}.

Required OAuth scope: web-packages:write