 Implement User Roles and Permissions

**Type**: Feature, Security  
**Priority**: Critical  
**Labels**: `feature`, `security`, `authorization`

**Description**:
Add comprehensive role-based access control (RBAC).

**Roles to Support**:
- Admin
- Manager
- Operator
- Viewer
- Custom roles

**Acceptance Criteria**:
- RBAC fully implemented
- Permission checks on all operations
- Role management UI
- All CI/CD checks must pass

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