feat(ui): improve Header layout with tag-aware padding and renamed sections

- Add data-has-tags attribute to reduce header padding-top when tags are present
- Rename beforeSticky/afterSticky classes to headerTop/headerBottom
- Always render headerBottom for consistent bottom margin
- Inline JSX sections into a single return statement

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

.storybook/themes/spotify.css

@@ -246,17 +246,16 @@
  */
 [data-theme-name='spotify'] {
   .bui-PluginHeaderToolbar {
-    padding: 0;
     height: 32px;
     border: none;
     background: none;
-    margin-bottom: var(--bui-space-2);
+    margin-top: var(--bui-space-4);
   }
 
   .bui-PluginHeaderTabsWrapper {
-    padding: 0;
     border: none;
     background: none;
-    margin-left: -8px;
+    margin-left: 0;
+    margin-top: var(--bui-space-2);
   }
 }