refactor: remove coexistence mode, use React only

Remove all dual-mode rendering logic since React is now the single
admin interface. Focus on implementing full table features in React.

Changes:
- Remove ?react= query param checks from all page methods
- Remove admin notice and footer toggle from ReactAdmin
- Simplify asset loading - ReactAdmin handles all assets
- Clean up Init.php enqueue method

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

includes/Init.php

@@ -80,18 +80,6 @@ class Init {
     public function enqueue() {
         global $current_screen;
 
-        // Check coexistence mode - if React is active, don't load classic shared assets
-        $use_react = isset($_GET['react']) || get_option('formipay_use_react_admin', false);
-        $is_formipay_screen = strpos($current_screen->id, 'formipay') !== false;
-
-        // Don't load classic Grid.js/shared assets when React is active on admin pages
-        if ($use_react && $is_formipay_screen && $current_screen->base !== 'post') {
-            // Still load SweetAlert2 for React mode (needed for modals)
-            wp_enqueue_style( 'sweetalert2', FORMIPAY_URL . 'vendor/SweetAlert2/sweetalert2.min.css', [], '11.14.4', 'all');
-            wp_enqueue_script( 'sweetalert2', FORMIPAY_URL . 'vendor/SweetAlert2/sweetalert2.min.js', ['jquery'], '11.14.4', true);
-            return;
-        }
-
         $formipayCPTs = [
             'formipay-form' => __( 'Edit Form', 'formipay' ), 
             'formipay-product' => __( 'Edit Product', 'formipay' ),