Create flow centralization and cleanup

app/(app)/create/utils/flowSteps.ts

@@ -117,6 +117,26 @@ export function getStepIndex(step: CreateFlowStep | null | undefined): number {
   return FLOW_STEP_ORDER.indexOf(step);
 }
 
+/**
+ * Steps where below `lg` the main column scrolls with split layout
+ * (`CreateFlowLayoutClient` — Linear CR-92 §4).
+ */
+export const CREATE_FLOW_SELECT_SPLIT_SCROLL_STEPS: readonly CreateFlowStep[] = [
+  "community-size",
+  "community-structure",
+  "core-values",
+  "decision-approaches",
+] as const;
+
+export function createFlowStepUsesSelectSplitScroll(
+  step: CreateFlowStep | null | undefined,
+): boolean {
+  if (!step) return false;
+  return (CREATE_FLOW_SELECT_SPLIT_SCROLL_STEPS as readonly string[]).includes(
+    step,
+  );
+}
+
 /**
  * Whether the given string is a valid create flow step
  */