Deletes an asset relationship by asset_relationships.relationship_id for the authenticated tenant. The service hard-deletes rows where relationship_id and context.tenant match, publishes no event, and performs no existence check; missing or cross-tenant IDs are silent no-ops. The controller intends to return 204 with no body, but currently constructs a JSON response with status 204, which can throw in NextResponse. In the current route wiring, req.context may also be absent because no route-level API-key auth wrapper sets it, causing a 500 before deletion.