feat: Add license management and tabbed settings (v0.3.0)

- Implement license management using magdev/wc-licensed-product-client
- Reorganize settings page into License, Default Settings, Integrations tabs
- Add license validation and activation via AJAX
- Frontend features require valid license (admin works always)
- Update translations with German (de_CH) for license strings

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

assets/js/admin.js

@@ -8,7 +8,115 @@
     'use strict';
 
     $(document).ready(function() {
-        // Admin scripts will be added here
+        // License validation functionality
+        initLicenseValidation();
     });
 
+    /**
+     * Initialize license validation AJAX handlers.
+     */
+    function initLicenseValidation() {
+        var $validateBtn = $('#fedistream-validate-license');
+        var $activateBtn = $('#fedistream-activate-license');
+        var $spinner = $('#fedistream-license-spinner');
+        var $message = $('#fedistream-license-message');
+
+        if (!$validateBtn.length) {
+            return;
+        }
+
+        // Validate license button
+        $validateBtn.on('click', function(e) {
+            e.preventDefault();
+            performLicenseAction('fedistream_validate_license', 'Validating...');
+        });
+
+        // Activate license button
+        $activateBtn.on('click', function(e) {
+            e.preventDefault();
+            performLicenseAction('fedistream_activate_license', 'Activating...');
+        });
+
+        /**
+         * Perform license AJAX action.
+         *
+         * @param {string} action AJAX action name.
+         * @param {string} loadingText Loading button text.
+         */
+        function performLicenseAction(action, loadingText) {
+            var originalText = $validateBtn.text();
+
+            // Show loading state
+            $spinner.addClass('is-active');
+            $validateBtn.prop('disabled', true);
+            $activateBtn.prop('disabled', true);
+            $message.hide();
+
+            $.ajax({
+                url: ajaxurl,
+                type: 'POST',
+                data: {
+                    action: action,
+                    nonce: fedistreamLicenseNonce
+                },
+                success: function(response) {
+                    $spinner.removeClass('is-active');
+                    $validateBtn.prop('disabled', false);
+                    $activateBtn.prop('disabled', false);
+
+                    if (response.success) {
+                        showMessage('success', response.data.message);
+                        // Reload page to show updated status
+                        setTimeout(function() {
+                            window.location.reload();
+                        }, 1500);
+                    } else {
+                        showMessage('error', response.data.message || 'An error occurred.');
+                    }
+                },
+                error: function(xhr, status, error) {
+                    $spinner.removeClass('is-active');
+                    $validateBtn.prop('disabled', false);
+                    $activateBtn.prop('disabled', false);
+                    showMessage('error', 'Request failed. Please try again.');
+                }
+            });
+        }
+
+        /**
+         * Show a message to the user.
+         *
+         * @param {string} type Message type: 'success', 'error', 'warning', 'info'.
+         * @param {string} text Message text.
+         */
+        function showMessage(type, text) {
+            var classMap = {
+                'success': 'notice-success',
+                'error': 'notice-error',
+                'warning': 'notice-warning',
+                'info': 'notice-info'
+            };
+
+            var noticeClass = classMap[type] || 'notice-info';
+
+            $message
+                .removeClass('notice-success notice-error notice-warning notice-info')
+                .addClass('notice ' + noticeClass)
+                .html('<p>' + escapeHtml(text) + '</p>')
+                .show();
+        }
+
+        /**
+         * Escape HTML entities.
+         *
+         * @param {string} text Text to escape.
+         * @return {string} Escaped text.
+         */
+        function escapeHtml(text) {
+            var div = document.createElement('div');
+            div.textContent = text;
+            return div.innerHTML;
+        }
+    }
+
 })(jQuery);