v0.1.30-pre.78

preview: nothing a person can see changes in this one, and it is provable rather than claimed:
the animated-image decode on the desktop and in the browser now takes its thread context from
the session instead of naming a pool itself, and in every installable build that context is the
same pool it always used. The build check that refuses a screen picking its own pool now covers
every production source set in the ui module, which ends that class there.

No migration: schema stays at 22 as at pre.77, so an account this build opens still needs
pre.61 or newer. Going back below that drops you at the account picker as though the account
were gone.

Landed from pr-stetson, pull request 42792544 at tip ce9c4077, merge 7af19b0d. Fixes #1cf448aa.