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/css/admin.css

@@ -4,4 +4,122 @@
  * @package WP_FediStream
  */
 
-/* Admin styles will be added here */
+/* Settings page tabs */
+.nav-tab-wrapper + .fedistream-settings-content {
+    margin-top: -1px;
+}
+
+.fedistream-settings-content {
+    background: #fff;
+    border: 1px solid #c3c4c7;
+    border-top: none;
+    padding: 20px;
+}
+
+/* Active tab styling */
+.wrap .nav-tab-wrapper .nav-tab-active {
+    background: #fff;
+    border-bottom-color: #fff;
+}
+
+/* License status banner */
+.fedistream-license-status {
+    margin-bottom: 20px;
+}
+
+.fedistream-license-status .dashicons {
+    color: inherit;
+}
+
+.fedistream-license-status.notice-success .dashicons {
+    color: #00a32a;
+}
+
+.fedistream-license-status.notice-error .dashicons {
+    color: #d63638;
+}
+
+.fedistream-license-status.notice-warning .dashicons {
+    color: #dba617;
+}
+
+.fedistream-license-status.notice-info .dashicons {
+    color: #72aee6;
+}
+
+/* License form buttons */
+#fedistream-license-form .button .dashicons {
+    font-size: 16px;
+    width: 16px;
+    height: 16px;
+    line-height: 1.3;
+}
+
+/* License message display */
+#fedistream-license-message {
+    padding: 10px 15px;
+}
+
+#fedistream-license-message p {
+    margin: 0;
+}
+
+/* Dashboard stats grid */
+.fedistream-stats {
+    display: grid;
+    grid-template-columns: repeat(4, 1fr);
+    gap: 20px;
+    margin: 20px 0;
+}
+
+.fedistream-stat-box {
+    background: #fff;
+    padding: 20px;
+    border: 1px solid #ccd0d4;
+    border-radius: 4px;
+}
+
+.fedistream-stat-box h3 {
+    margin: 0 0 10px;
+}
+
+.fedistream-stat-box p {
+    font-size: 2em;
+    margin: 0;
+    color: #2271b1;
+}
+
+/* Quick actions */
+.fedistream-quick-actions {
+    background: #fff;
+    padding: 20px;
+    border: 1px solid #ccd0d4;
+    border-radius: 4px;
+    margin: 20px 0;
+}
+
+/* Info box */
+.fedistream-info {
+    background: #fff;
+    padding: 20px;
+    border: 1px solid #ccd0d4;
+    border-radius: 4px;
+}
+
+/* Responsive adjustments */
+@media screen and (max-width: 782px) {
+    .fedistream-stats {
+        grid-template-columns: repeat(2, 1fr);
+    }
+
+    #fedistream-license-form .button {
+        display: block;
+        margin: 10px 0 0 0 !important;
+    }
+}
+
+@media screen and (max-width: 480px) {
+    .fedistream-stats {
+        grid-template-columns: 1fr;
+    }
+}