Move hand-rolled dialog overlays onto the shared Dialog component #1854

Follow-up to the lint sweep (#1743). The sweep gave the ad-hoc overlays dialog roles, Escape and focus handling (CertificateCleanupDialog, ImportSuccessModal, WafConfig ConfirmDialog, CrowdSec ban/unban modals, ProxyHostForm, Uptime, UsersPage). They still duplicate src/components/ui/Dialog.tsx (Radix: focus trap, portal, scroll lock). Migrating them removes the duplication but changes DOM and focus behaviour, so it needs its own PR and E2E checks. ProxyHostForm and Uptime dialogs have no Escape handler on purpose (unsaved input). Severity: low.