Google Calendar integration for booking notifications

- New GoogleCalendar library: createEvent/updateEvent/deleteEvent via service account, all wrapped in try/catch so failures never break booking flow
- booking_process: creates worker + owner calendar events on new booking
- manage_booking_process: deletes old events, creates new ones on modify
- manage_booking_cancel: deletes events before cancellation
- Service_model: updateBookingCalEvents() stores gcal event IDs
- Admin worker form: Google Calendar ID field added
- PHPMailer: enabled exceptions (was silently swallowing SMTP errors)
- Config: application/config/google_calendar.php for service account path + Evelin calendar ID

DB migration required:
  ALTER TABLE workers ADD COLUMN google_calendar_id VARCHAR(255) NULL DEFAULT NULL;
  ALTER TABLE bookings ADD COLUMN gcal_event_id_worker VARCHAR(255) NULL DEFAULT NULL;
  ALTER TABLE bookings ADD COLUMN gcal_event_id_owner VARCHAR(255) NULL DEFAULT NULL;

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

composer.json

@@ -11,7 +11,9 @@
 		"source": "https://github.com/bcit-ci/CodeIgniter"
 	},
 	"require": {
-		"php": ">=5.3.7"
+		"php": ">=5.3.7",
+		"google/apiclient": "^2.0",
+		"phpmailer/phpmailer": "^6.0"
 	},
 	"suggest": {
 		"paragonie/random_compat": "Provides better randomness in PHP 5.x"