Google Calendar: Domain-Wide Delegation support for attendee invitations

Service account can now impersonate a Workspace user (set gcal_impersonate_email
in config) to unlock attendee invitations with push notifications.
Falls back to silent event creation if impersonation is not configured.

Setup required in Google Admin Console:
  Security → API Controls → Domain-wide delegation
  → Add service account client_id with scope:
  https://www.googleapis.com/auth/calendar

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

application/config/google_calendar.php

@@ -3,3 +3,4 @@ defined('BASEPATH') OR exit('No direct script access allowed');
 
 $config['gcal_service_account_path'] = APPPATH . 'config/service-account-key.json';
 $config['gcal_evelin_calendar_id']   = 'katozoltan0804@gmail.com'; // Evelin's Calendar ID (e.g. her Gmail address)
+$config['gcal_impersonate_email']    = ''; // Workspace user to impersonate (e.g. evelin@studiobeve.no) — required for attendee invitations