Bring LiteLLM into the two-tier RBAC and map groups to LiteLLM roles.
- akP-litellm-admin / akP-litellm-user permission groups (bound to the litellm
app for access); added to akR-global-admin / akR-standard-user roles.
- Generic per-provider role_mappings: emit an app role claim computed from
effective (hierarchical) group membership. LiteLLM: emits `litellm_role`
(proxy_admin for akP-litellm-admin, internal_user for akP-litellm-user, else
internal_user_view_only); LiteLLM reads it via GENERIC_USER_ROLE_ATTRIBUTE.
Validated: plan 5 to add, 3 to change; generated role expression renders correctly.