Only one copy of the app runs at a time now — the goodnight kiss

If you're signed in and open the app in a second tab, or another browser, or another machine, the older copy puts up a friendly dialog: the app is running in another tab, click OK to reload this one, or close it, no work lost. This fixes a bug that bit quietly and repeatedly: a change you made in one place — say, the URL of your icon in settings — could be silently wiped when an older copy, still running with the old settings, saved over it. Now a stale copy stands down the moment a fresh one signs on, so your latest settings always win. When the app connects, it identifies you to the server, and the server sends a "goodnight" message to every other connection you have open — the name comes from that message. (Client v0.6.7.)