Update RBAC creator/purger patterns to align with BEP-1048

## Summary

Update the RBAC repository base patterns (`repositories/base/rbac/`) to align with BEP-1048 Entity Relationship Model.

## Background

BEP-1048 unifies all entity relationships into `association_scopes_entities` with explicit `relation_type` (auto/ref), replacing scattered tables (`entity_fields`, `object_permissions`). The current RBAC creator/purger patterns need updates to match this design.

## Scope

1. entity_creator — Add relation_type support
1. entity_purger — Bidirectional edge cleanup + table migration
1. field_creator / field_purger — Remove (replaced by entity_creator)
1. granter — Migrate from object_permissions to permissions table
1. revoker — Migrate from object_permissions to permissions table

## Related

- BEP: BEP-1048 (proposals/BEP-1048-RBAC-entity-relationship-model.md)
- Parent Epic: BA-4179

JIRA Issue: BA-4454