Clean up RBAC legacy code

Remove deprecated RBAC tables, models, and business logic that have been superseded by the BEP-1048 entity relationship model.

Includes:

- BA-4360: Remove object permissions table and business logic

- BA-4361: Remove role_manager and update db/repository functions for new RBAC schema

Future candidates (as RBACElementType migration progresses):

- Remove ScopeType enum (replaced by RBACElementType)

- Remove RBAC subset of EntityType (replaced by RBACElementType)

- Remove ScopeId/ObjectId in RBAC contexts (replaced by RBACElementRef)

Reference:

- BEP-1048: RBAC Entity Relationship Model

- BA-4179: Implement RBAC Entity Relationship Model

- BA-4521: Unify RBAC type system

JIRA Issue: BA-4622