feat(ui): add Guidelines section with Cards + Table page layout story

- Add `packages/ui/src/guidelines/CardsWithTable.stories.tsx` as the
  first guideline story, showing three data-driven metric cards in a
  3-column grid above a paginated table of catalog services.
- Update Storybook `storySort` order so the new `Guidelines` group
  appears at the top of the `Backstage UI` section.
- Wrap story content in a `Box bg="neutral-1"` when the Spotify theme
  is active, preserving `layout: centered` centering and always
  applying `borderRadius`.
- Import `Box` from the UI package into the Storybook preview.
- Remove `transition` from `Container` CSS to avoid animation on resize.
- Set `padding-inline: 0` on `.bui-Container` inside the Spotify theme
  so containers render flush within the themed wrapper.

Signed-off-by: Charles de Dreuille <charles.dedreuille@gmail.com>
Co-authored-by: Cursor <cursoragent@cursor.com>

.storybook/themes/spotify.css

@@ -213,6 +213,10 @@
   .bui-Tag {
     border-radius: var(--bui-radius-full);
   }
+
+  .bui-Container {
+    padding-inline: 0;
+  }
 }
 
 [data-theme-mode='light'][data-theme-name='spotify'] {