FIX: resolve npm path in prepare_package.py on Windows (#1629)

Co-authored-by: Adrian Gavrila <agavrila@microsoft.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: 3 people

build_scripts/prepare_package.py

@@ -48,7 +48,7 @@ def build_frontend(frontend_dir: Path) -> bool:
     print("\nInstalling frontend dependencies...")
     try:
         subprocess.run(
-            ["npm", "install", "--legacy-peer-deps"],
+            [npm, "install", "--legacy-peer-deps"],
             cwd=frontend_dir,
             check=True,
             stdout=subprocess.PIPE,