site-setup: hide the Back button on the entry steps instead of exiting home

Following the removal of the goals step's inbound links, the design picker
and import capture steps had their Back buttons repointed to exit to the
site home. A Back button that jumps out to /home is more confusing than no
Back button, and both are entry steps with nothing before them.

Omit goBack for those steps so the shared step chrome hides the Back button.
The design picker's back handler now mirrors that: it renders a back
affordance only when the flow supplies one, keeping the shared design picker
free of flow-specific knowledge.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: taipeicoder

client/landing/stepper/declarative-flow/flows/site-setup-flow/site-setup-flow.ts

@@ -391,9 +391,6 @@ const siteSetupFlow: Flow = {
 			}
 
 			switch ( currentStep ) {
-				case 'design-setup':
-					return exitFlow( `/home/${ siteId ?? siteSlug }` );
-
 				case 'importList': {
 					if ( backToStep ) {
 						return navigate( `${ backToStep }?siteSlug=${ siteSlug }` );
@@ -453,9 +450,6 @@ const siteSetupFlow: Flow = {
 				case 'importReadyPreview':
 					return navigate( `import?siteSlug=${ siteSlug }` );
 
-				case 'import':
-					return exitFlow( `/home/${ siteId ?? siteSlug }` );
-
 				case 'verifyEmail':
 				case 'trialAcknowledge':
 					return navigate( `importerWordpress?${ urlQueryParams.toString() }` );
@@ -485,7 +479,18 @@ const siteSetupFlow: Flow = {
 			}
 		};
 
-		return { goNext, goBack, goToStep, submit, exitFlow };
+		// The design picker and import capture are the flow's entry steps, so
+		// there is nothing to go back to — omit goBack to hide the Back button
+		// rather than send the user out to the site home.
+		const isEntryStep = currentStep === 'design-setup' || currentStep === 'import';
+
+		return {
+			goNext,
+			goBack: isEntryStep ? undefined : goBack,
+			goToStep,
+			submit,
+			exitFlow,
+		};
 	},
 
 	useAssertConditions(): AssertConditionResult {

client/landing/stepper/declarative-flow/internals/steps-repository/design-setup/unified-design-picker.tsx

@@ -426,12 +426,13 @@ const UnifiedDesignPickerStep: StepType< {
 		if ( isComingFromSuccessfulImport ) {
 			return undefined;
 		}
-		return intent === 'update-design'
-			? () =>
-					submit?.( {
-						eventProps: commonFilterProperties,
-					} )
-			: () => handleBackClick();
+		if ( intent === 'update-design' ) {
+			return () =>
+				submit?.( {
+					eventProps: commonFilterProperties,
+				} );
+		}
+		return goBack ? () => handleBackClick() : undefined;
 	};
 
 	const backButton = getGoBackHandler();