If ssr: false is set for all pages then automatically pre-render them

[brillout]

Description

You should ensure that when the config item ssr:true, the built project can be run directly in the 'dist' directory by default in a way like 'node index.mjs'. When 'ssr:false', you should make sure that there is a 'index.html' in the default state (not prerender) that can be used directly by the web server.

See also: #1851.