Add a compliance dashboard for admin users

[Mystery-CLI]

🔧 Title: Add a compliance dashboard for admin users

📘 Description
frontend/src/components/ComplianceDashboard.jsx (8KB) exists but may only be accessible to all users. Compliance dashboards showing AML alerts, KYC queue, and sanctions matches should be restricted to admin/compliance officer roles.

✅ Acceptance Criteria

• Add a role field to the User model: USER, COMPLIANCE, ADMIN
• Restrict ComplianceDashboard to users with COMPLIANCE or ADMIN role
• Add role-based access control middleware to all compliance API endpoints
• Add a role assignment endpoint (admin only)
• Add tests for role-based access control

🔧 Context: frontend/src/components/ComplianceDashboard.jsx; backend/src/routes/compliance.js.

---