[Release Docs] Docs for removing delete button when this action is prohibited #651

This issue adds user-facing documentation for the delete-guardrail behavior on competency data.

Documentation should explain why a delete/remove action can become disabled (deletion is prohibited once competency taxonomy data — criteria, criteria groups, rule profiles, tags, taxonomies, or object tag associations — has associated student mastery statuses), which pages this appears on (Competency Management, Taxonomy Editing, Course Outline), and what an admin or course author should do instead (e.g., MVP has no archiving; the data stays in place). Documentation should follow the same process used for the previous taxonomy editing work, with docs added to the Open edX documentation repository.

Release notes are not expected to be created as part of this ticket. Axim is experimenting with generating release notes separately, and the team may share those for review if needed.

Documentation Location:
Documentation should be added to the Open edX documentation repository:
https://github.com/openedx/docs.openedx.org

Outstanding/Needs Confirmation:

• Confirm the exact documentation page or section where this content should be added in the repository.
• Confirm this doc is written against the finalized UI (depends on tickets 8, 9, and 10 in this set landing first).