chore(Icon stories): drop #888 backdrop from IconHarness

The IconHarness wrapper applied a hardcoded grey #888 background that
made sense for Spacer/Separator (where you need contrast against an
otherwise invisible primitive) but hurt Icon's stories — it muddied
the state pills (success/warning/danger/info badges) and washed out
glyphs whose visibility doesn't need any artificial contrast against
Storybook's page background.

Drop the backdrop and the 24px padding; keep the wrapper as a
testid-only inline-flex container so the Playwright locator still
attaches. All 36 Icon snapshots regenerated.

No component code changes; stories/spec layout only.

Author: DreaminDani

src/components/Icon/Icon.stories.tsx

@@ -59,11 +59,7 @@ export const Playground: Story = {
 const IconHarness = (props: ImageType) => (
   <div
     data-testid="icon-harness"
-    style={{
-      display: 'inline-flex',
-      padding: '24px',
-      background: '#888',
-    }}
+    style={{ display: 'inline-flex' }}
   >
     <Icon {...props} />
   </div>