Add privacy-friendly analytics and cookie consent, integrated into the CMS

Adds a first-party analytics system with no third-party trackers and no
persistent per-visitor identifiers: events are grouped into sessions via a
daily-rotating pseudonymous hash (IP+UA+host, HMAC-salted, never stored raw).

- New "Analytics" section in the Payload admin, gated by a canViewAnalytics
  permission on Users, following the existing custom-admin-view pattern
  used by the calendar feature
- Sessions, page views, unique visitors, top/entry/exit pages, events,
  device/browser breakdown, date range filter with period comparison
- Raw events and daily aggregate rollups as their own collections, with
  configurable retention and a cron endpoint that rolls up before purging
- Cookie consent banner (necessary/preferences/statistics) with categories
  and copy editable from a new CMS global; a track() helper that is a
  complete no-op without statistics consent, so nothing is ever sent
  before a visitor opts in
- track() calls wired into the booking flow, contact form, and navigation

.env.example

@@ -25,6 +25,11 @@ PAYLOAD_SECRET=replace-with-a-long-random-secret
 # Generate with: openssl rand -hex 32
 MEETING_SESSION_SECRET=replace-with-a-long-random-secret
 
+# Salts the daily-rotating, non-reversible visitor hash used for Analytics
+# session grouping (kept separate from PAYLOAD_SECRET on purpose, see
+# lib/analytics/salt.ts). Generate with: openssl rand -hex 32
+ANALYTICS_SALT_SECRET=replace-with-a-long-random-secret
+
 # Sent as "Authorization: Bearer <value>" by the external cron job that
 # triggers /api/cron/event-reminders. Generate with: openssl rand -hex 32
 CRON_SECRET=replace-with-a-long-random-secret