fix(onboarding): hide color picker when a starter site has a single palette

The per-card color swatch summary rendered whenever a site had at least one
color, showing a lone non-actionable dot when there was nothing to choose.
Only render the picker when there are 2+ palettes (colorOptions.length > 1).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QrGf4K9upxDKhRPVCztoLs

Author: ineagu

onboarding/src/Components/StarterSiteCard.js

@@ -194,7 +194,7 @@ const StarterSiteCard = ( {
 								) ) }
 							</div>
 						) }
-						{ colorOptions.length > 0 && (
+						{ colorOptions.length > 1 && (
 							<div
 								className={
 									isColorExpanded