Casbin ABAC Integration (stub)

This guide will cover:

• Migrating from the current RBAC model to Casbin Attribute-Based Access Control (ABAC)
• Defining ABAC policies in casbin_model.conf and casbin_policy.csv
• Evaluating permissions against dynamic attributes (org_id, resource_owner, time_of_day)
• Backward compatibility with existing RBAC roles during migration