No longer abuse the desk field, instead making use of the path. Reject
any scries outside of the local ship, empty desk and current time as
invalid.
Expose ducts only under a debug endpoint, nothing else should care about
being able to inspect them.
Add scry endpoints for the very next timer (if any), and all timers up
to and including a specified timestamp.
Associates channels with the authentication sessions that opened them,
and deletes the channel when its associated session expires.
Also updates the debug dashboard to display channel counts per session.
