[Change Requests] - Remove leadership change requests

Description

Context

Leadership CRs (CR_Type.LEADERSHIP) are being removed as part of phasing out auto-implementing CR types. The creation path (createLeadershipChangeRequest / applyLeadershipChangeRequest) needs to go, along with references to LEADERSHIP in reviewer-queue filtering. Since CR_Type is a Postgres enum and historical rows will already have type: LEADERSHIP, the enum value and the Leadership_CR model must stay for historical/audit purposes only the ability to create new ones is being removed.

Task

Remove createLeadershipChangeRequest and applyLeadershipChangeRequest. Remove CR_Type.LEADERSHIP from the exclusion filter in getToReviewChangeRequests and from the OR clause in getApprovedChangeRequests. Remove any routes, frontend entry points, and shared-type references used to create a leadership CR. Do not remove the LEADERSHIP enum value or the Leadership_CR model/relations leave those intact for historical reads.

Acceptance Criteria

• No route or UI path exists to create a new leadership CR.
• Existing leadership CRs still display correctly wherever CR history is shown.
• getToReviewChangeRequests and getApprovedChangeRequests no longer reference CR_Type.LEADERSHIP in dead filter branches.

Search for createLeadershipChangeRequest, applyLeadershipChangeRequest, CR_Type.LEADERSHIP, and the getToReviewChangeRequests and getApprovedChangeRequests entry points, then trace their routes, frontend entry points, and shared types. Done means creation paths and dead filter references are removed while the LEADERSHIP enum value, Leadership_CR model and relations, and historical displays remain intact.