ACL support — owner, manage, and use roles

[Rampim]

Description

Implement access control from Unity Catalog ACL model to enforce permission levels within the app.

Roles

• Owner — full control (create/delete gateways, manage users, configure settings)
• Manage — configure gateways, view cache, clear cache
• Use — query only (submit questions, view results)

Scope

• Define role model and permission matrix
• Integrate with Databricks workspace identity (OAuth user)
• Enforce permissions on gateway CRUD and query endpoints
• Role assignment UI in frontend