kiln: install from existing desks during +on-init
kiln: install from existing desks during +on-init

During kiln's +on-init, we now check for non-base (and non-kids) desks.
If any are present, we execute the install flow for them, and set them
to sync from our sponsor afterwards.

This depends on work done in d7afe3229, in that without those changes
the successive +find requests from kiln to clay would clobber each
other, leaving only the "install from sponsor" one active, thus never
actually installing the desk for which we already have the files.

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