feat(GRO-1794): add booking funnel analytics events

- New analytics utility (src/lib/analytics.ts) with ANALYTICS_EVENTS constants
  and fireAnalyticsEvent() – thin wrapper over window.dispatchEvent, no-op safe
  Built for Plausible/GTM integration later.

- Public booking wizard (Book.tsx): fires step-transition events at each step
  (service → time → contact → submit) plus booking_confirmed on the dedicated
  confirmation page.

- Portal BookingFlow (Appointments.tsx): fires equivalent events for the
  portal booking flow. booking_confirmed fires via useEffect when the inline
  success state is shown.

- BookingErrorPage: fires booking_error on mount (no PII in payload).

Events include step name and flow type (public/portal) but contain no PII:
no names, emails, phone numbers, or pet names in any payload.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/pages/BookingError.tsx

@@ -1,4 +1,6 @@
+import { useEffect } from "react";
 import { BUSINESS_CONTACT_INFO } from "../lib/contact";
+import { ANALYTICS_EVENTS, fireAnalyticsEvent } from "../lib/analytics";
 
 const STRINGS = {
   heading: "Link Invalid or Expired",
@@ -9,6 +11,10 @@ const STRINGS = {
 } as const;
 
 export function BookingErrorPage() {
+  useEffect(() => {
+    fireAnalyticsEvent(ANALYTICS_EVENTS.BOOKING_ERROR, { step: "error", flow: "public" });
+  }, []);
+
   return (
     <div
       style={{