[BUG]: After packaging, exp9 files fail to open sub-pages such as 'receiver'

[Rain624]

Package version

3.1.0-exp.8

Environment

* OS:windwow
* Unity version:
* Graphics API:
* Browser:Google

Steps To Reproduce

1、Download exp9
2、Package the contents of the webapp folder into an EXE using npm
3、Double-click the .exe file to launch the web page, then click on 'Receiver Sample'.
4、Error：Cannot GET /receiver/index.html

Current Behavior

No response

Expected Behavior

No response

Anything else?

No response