nemo 0.3.0

Added

• Every release publishes the server image to ghcr.io/13/nemo, tagged with
  the version, its minor series and latest, so running the server is a pull
  rather than a clone and a build.
• Every screen says whether an account is connected, beside the settings
  button: the account's initial when there is one, a way in when there is
  not, and a warning when the session has expired.

Changed

• The web app asks who you are before it shows anything, and signing out of
  it clears the browser rather than leaving one person's tasks behind for
  the next. The Android app is unchanged: an account is still optional,
  and signing out keeps your tasks on the device.

Fixed

• Android can reach a server whose certificate comes from a certificate
  authority of your own. Dart's HTTP client reads only the system
  certificate store, so an authority installed on the device was invisible
  to it and every connection failed as "could not reach the server". The
  app now shows the certificate the server offered -- who issued it, how
  long it is good for, and its SHA-256 fingerprint -- and asks. What you
  accept is pinned to that certificate on that host; a renewed one asks
  again.