WIP Add settings/about pane

app/components/app-header.gjs

@@ -23,7 +23,12 @@ export default class AppHeaderComponent extends Component {
   <template>
     <header class="app-header">
       <div class="header-left">
-        <button class="icon-btn" type="button" aria-label="Menu">
+        <button
+          class="icon-btn"
+          type="button"
+          aria-label="Menu"
+          {{on "click" @onToggleMenu}}
+        >
           <Icon @name="menu" @size={{24}} @color="#333" />
         </button>
       </div>

app/components/settings-pane.gjs

@@ -0,0 +1,20 @@
+import Component from '@glimmer/component';
+import { on } from '@ember/modifier';
+import Icon from '#components/icon';
+
+export default class SettingsPane extends Component {
+  <template>
+    <div class="sidebar settings-pane">
+      <div class="sidebar-header">
+        <h2>Settings</h2>
+        <button type="button" class="close-btn" {{on "click" @onClose}}>
+          <Icon @name="x" @size={{20}} @color="#333" />
+        </button>
+      </div>
+
+      <div class="sidebar-content">
+        <p>Settings content placeholder...</p>
+      </div>
+    </div>
+  </template>
+}