chore: lock the plugin boundary and remove 2.9.0 leftovers

plugins/file-manager/src/frontend/components/DraggableWindow.tsx

@@ -1,5 +1,5 @@
 import React, { useState, useRef, useCallback, useEffect } from "react";
-import { cn } from "@/lib/utils.ts";
+import { cn } from "@termix/plugin-sdk/ui";
 import { Minus, X, Maximize2, Minimize2 } from "lucide-react";
 import { useTranslation } from "react-i18next";