Add role-based UI permission gating

[Dannyswiss1]

client/src/lib/types.ts already defines StaffRole (admin | clinician | front_desk), but nothing in the UI
uses it — every connected wallet sees every action. Gate sensitive actions (revoking access, uploading records,
adding/removing staff) behind role checks, and reflect the current user's effective role somewhere visible in the
UI (e.g. the Navbar or Provider Profile).

Acceptance criteria

• front_desk role cannot upload records or revoke access grants (buttons hidden or disabled with a tooltip)
• admin-only actions (staff management) are gated to admin role
• Current effective role is visibly surfaced somewhere in the UI