This PR is a follow-up on #9741

Original Description

global sidebard is detected by undefined id, so we need to compute id from title not too early, and in a a way that does not modify initial config

• Closes Sidebar not displayed if no Quarto document #9242
• Closes Sidebar not loading properly in new version, works in old version #9728
• Closes Book 404 page does not include book navbar preventing navigation #10014

This is currently a proposal built on top of unmerged #8871 by @dragonstyle to deal with #8869 and follow up on #5689

I believe we can do what was supposed to be done in #8871, but we need to make sure that we don't modify initial navigation.sidebars content's id.

I still think we could consider adding a more explicit global config for true or false to make this more clear.

This requires some testing to be sure it works ok this time. Opening this draft PR to discuss and have thoughts on this change.

New consideration

This PR broke complex website like Quarto web. So this type of change needs to be tested against very complex usage of sidebar.
So the implicit global sidebar detection is still not working - maybe adding a new global config kye is better than considering id to be undefined as a global sidebar.

Opening as a draft to remember work done, and try again later.

TO DO

• Add more test to reproduce quarto.org breakage
• Test on other complex website
• Consider a global: true key in sidebar per sidebar with single sidebar entry gets shown across entire website #5689 (comment)