Add button and custom modal flow implemented

lib/create/reorderCustomMethodCardFieldBlocks.ts

@@ -0,0 +1,18 @@
+/**
+ * Immutable reorder for custom method card field blocks (wizard step 3, edit modal).
+ */
+export function reorderCustomMethodCardFieldBlocks<T>(
+  blocks: readonly T[],
+  fromIndex: number,
+  toIndex: number,
+): T[] {
+  if (fromIndex === toIndex) return [...blocks];
+  if (fromIndex < 0 || toIndex < 0 || fromIndex >= blocks.length) {
+    return [...blocks];
+  }
+  if (toIndex >= blocks.length) return [...blocks];
+  const next = [...blocks];
+  const [removed] = next.splice(fromIndex, 1);
+  next.splice(toIndex, 0, removed);
+  return next;
+}