devtools custom tab ignores app baseURL

[jdhartley]

Describe the bug
When opening the tab on an app that uses a baseURL, the devtools <iframe> loads the incorrect URL

The DEVTOOLS_UI_PATH is set to '/__nuxt-devtools-fonts' but should support '/prefix/__nuxt-devtools-fonts' when a baseURL is defined

To reproduce
Set up your nuxt config with

	app: {
		baseURL: '/prefix/',
	},

You will see the <iframe src> is lacking the baseURL. This is most noticeable when your app is served via a proxy

Additional context
I have seen other libraries join nuxt.options.app.baseURL to fix

addCustomTab({
  view: {
    type: 'iframe',
    src: joinURL(nuxt.options.app?.baseURL, '/__nuxt-devtools-fonts'),

I will try to submit a PR with a fix but wanted to open this issue first