E2E: Sessions inspection and revocation

[Bccorb]

Part of #176. Depends on #177.

Goal

Cover the Sessions page: inspecting active sessions and revoking them individually.

Scope

• List renders seeded active sessions with their metadata columns.
• Revoke a single session: confirm plus step-up, sends the revoke, and removes the row.
• Step-up failure aborts the revoke and surfaces the failure toast.
• Read-only admin sees no revoke control.
• Loading, empty, and error states render correctly.

Key files

src/pages/Sessions.tsx, src/hooks/useSessions.ts, src/hooks/useRevokeSession.ts, src/components/Table.tsx, src/components/ConfirmProvider.tsx.