Refactor: Update all remaining pages to use unified header template

- Updated 39 pages from old header01.php and header02.php includes
- All pages now use single configurable header.php with $headerStyle variable
- Light style (default): Most pages (login, register, trips, courses, etc.)
- Dark style: Coming from header01 original usage

Pages updated:
  - Admin pages: admin_*.php (10 files)
  - Booking pages: bookings.php, campsite_booking.php, etc.
  - Content pages: blog.php, blog_details.php, contact.php, events.php, etc.
  - User pages: account_settings.php, membership*.php, register.php, etc.
  - Utility pages: 404.php, payment_confirmation.php, reset_password.php, etc.

All pages now maintain single header template source - easier to update navigation, styles, and functionality across the entire site.

membership_payment.php

@@ -1,4 +1,6 @@
-<?php include_once('header02.php');
+<?php
+$headerStyle = 'light';
+include_once('header.php');
 // Assuming you have the user ID stored in the session
 if (isset($_SESSION['user_id'])) {
     $user_id = $_SESSION['user_id'];