Improve timezone handling (#18257)

* Ensure review activity calendar uses correct timezone

react-day-picker 9.x adds a timeZone prop and a TZDate() handler to show the calendar based on a timezone and better handle dates passed to it in timezones

* Ensure calendar range uses correct timezone

* clean up

* ensure range is timezone aware

* ensure export dates are timezone aware

web/src/components/overlay/ExportDialog.tsx

@@ -406,12 +406,14 @@ function CustomTimeSelector({
     config?.ui.time_format == "24hour"
       ? t("time.formattedTimestamp.24hour", { ns: "common" })
       : t("time.formattedTimestamp.12hour", { ns: "common" }),
+    config?.ui.timezone,
   );
   const formattedEnd = useFormattedTimestamp(
     endTime,
     config?.ui.time_format == "24hour"
       ? t("time.formattedTimestamp.24hour", { ns: "common" })
       : t("time.formattedTimestamp.12hour", { ns: "common" }),
+    config?.ui.timezone,
   );
 
   const startClock = useMemo(() => {