Create Role from Role Preset API

Add an API that instantiates a role from an existing role preset into a specified scope. Input: role_preset_id, scope_type, scope_id. The API takes a shallow snapshot of the preset (role + role_permission rows) into the target scope and copies preset.auto_assign onto the generated role; the instantiated role has no further relationship with the preset. This is a manual apply-a-preset-to-an-existing-scope operation, distinct from the auto-apply-at-scope-creation path. Full v2 stack: DTO, action + repository, GraphQL, REST v2.

JIRA Issue: BA-6323