feat(zone): add Cloudflare-style traffic overview charts

Expose Zone stats API with multi-host access-log aggregates and time
series, and render unique visitors, requests and data served on the
Zone overview with 24h/7d/30d range controls.

frontend/lib/services/openflare/index.ts

@@ -108,6 +108,9 @@ export type {
   ZoneItem,
   ZoneMutationPayload,
   ZoneOverview,
+  ZoneStats,
+  ZoneStatsPoint,
+  ZoneStatsRange,
   TlsCertificateApplyPayload,
   TlsCertificateContentItem,
   TlsCertificateDetailItem,