fix(ui): adjust plugin header spacing

Align PluginHeader spacing across tabbed and non-tabbed variants so the component owns the surrounding page spacing more consistently.

Signed-off-by: Charles de Dreuille <charles.dedreuille@gmail.com>

.storybook/themes/spotify.css

@@ -245,11 +245,12 @@
  * this file for easier scanning alongside other component overrides above.
  */
 [data-theme-name='spotify'] {
+  .bui-PluginHeader {
+    margin-top: var(--bui-space-4);
+  }
+
   .bui-PluginHeaderToolbar {
     height: 32px;
-    border: none;
-    background: none;
-    margin-top: var(--bui-space-4);
   }
 
   .bui-PluginHeaderTabsWrapper {
@@ -258,8 +259,4 @@
     margin-left: 0;
     margin-top: var(--bui-space-2);
   }
-
-  .bui-HeaderTop {
-    padding-top: var(--bui-space-4);
-  }
 }