Publish's %serve command makes builds for notes even if the
publish-info file is missing. It now crashes the build if the file is
missing with a one-line ?> asserting that the file is found in the
list of paths associated with the collection.
In Publish, users could get in a bad state if they made a post with
valid udon, and subsequently edited to contain invalid udon.
Furthermore, users subscribed to them would get in the same bad state.
This fixes the original bug, and users who are already in the broken
state will be able to run a recovery command: :publish %state-surgery
which will also fix the downstream broken state of their subscribers.
