Booking confirmation and calendar agree on displayed appointment time

When the booking confirmation email says "2 PM EST" and the calendar block says "7 PM UTC", the customer has no reliable signal about when to show up. This ISO 25010 functional-correctness failure typically stems from one component reading the raw UTC value while another converts it — two code paths, two different timezone assumptions, same appointment. The damage is a no-show or a wrong-time arrival, followed by a refund request and a support ticket. Confirmation-calendar parity is not cosmetic: it is the contract the customer relies on to plan their day.

Extract time formatting into a single shared utility function and call it from both the confirmation display and the calendar view — never format the same appointment time twice from different code paths.

// src/lib/format-appointment-time.ts
import { toZonedTime, format } from 'date-fns-tz'

export function formatAppointmentTime(utcDate: Date, tz: string): string {
  return format(toZonedTime(utcDate, tz), 'MMM d, yyyy h:mm a zzz', { timeZone: tz })
}

In src/components/BookingConfirmation.tsx and your confirmation email template in src/lib/email.ts, import and call formatAppointmentTime(appointment.start_time, appointment.customer_timezone). Remove any inline new Date().toLocaleString() calls that bypass the shared formatter.