Add Google Calendar sync: OAuth connect flow, dedicated Бронирования calendar, best-effort event create/update/delete on booking changes

.env.example

@@ -4,3 +4,12 @@
 ADMIN_BOOTSTRAP_EMAIL=admin@top-sysops.ru
 ADMIN_BOOTSTRAP_PASSWORD=
 ADMIN_BOOTSTRAP_NAME=Admin
+
+# Public origin this app is reachable at — must match exactly (scheme +
+# host, no trailing slash). Used to build the Google OAuth redirect URI.
+APP_URL=https://reser.top-sysops.ru
+
+# Google Cloud Console → APIs & Services → Credentials → OAuth client ID.
+# Add ${APP_URL}/api/google/callback as an authorized redirect URI there.
+GOOGLE_CLIENT_ID=
+GOOGLE_CLIENT_SECRET=