Implement frontend RBAC matching backend role system

[nullEFFORT]

Backend now has RBAC (analyst/operator/supervisor/admin). Frontend dashboard needs:

• Role-aware UI (hide/disable actions user cannot perform)
• Role indicator in navigation
• Admin panel for operator management
• Graceful handling of 403 responses

[nullEFFORT]

Backend RBAC is now complete (merged in #53). This issue now tracks only the frontend side:

• Hide/disable UI elements based on operator role
• Dashboard should call GET /api/auth/me to get current role
• Role hierarchy: analyst < operator < supervisor < admin
• Example: analyst should not see "Submit Report" button, operator should not see API key management

Backend enforces all restrictions regardless, so frontend is UX-only.