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

collections/Users.ts

@@ -45,6 +45,22 @@ export const Users: CollectionConfig = {
         update: isAdminFieldLevel,
       },
     },
+    {
+      name: "canViewAnalytics",
+      type: "checkbox",
+      label: "Analytics sichtbar",
+      defaultValue: true,
+      // Admins always have access regardless of this flag (see
+      // access/index.ts's canViewAnalytics) — this only matters once a
+      // non-admin role exists, letting an admin grant/revoke Analytics
+      // visibility per account without changing anyone's role.
+      access: {
+        update: isAdminFieldLevel,
+      },
+      admin: {
+        description: "Steuert, ob dieser Zugang das Analytics-Dashboard im Admin-Bereich sehen kann.",
+      },
+    },
     {
       name: "calendarFeedTokenHash",
       type: "text",