Make the website timezone aware

Render timestamps in the viewer's local timezone on the Economy Explorer.

Grounded: date/time formatting lives in economy-explorer/lib/format.ts (also used by Pagination, Footer, ActivityCalendar, charts). Because pages are SSR, timestamps currently format on the server (its tz/UTC), so a player abroad sees the wrong wall-clock time.

Make formatting timezone-aware: detect the viewer's tz (Intl resolved options client-side, or a tz cookie set on first load) and format against it — either hydrate the formatted strings client-side or pass the tz into the SSR formatter. Keep chart day-bucketing consistent with the chosen tz.