Chat onboarding bug collection

@jzila asked me to open a metabug with some buggy experiences I ran into, here's a list:

Bugs:

- When I first opened the chat app, it was stuck on the red "Rekeying device..." message until I switched tabs.
- I found a chat message was waiting for me from a friend, but I never received an out-of-band invitation/notification before I installed the app.
- I have a persistent [1 unread] in the tab/dock, but don't see any unread messages.
- Emojis don't show up in notifications (but rather as their string representations).

Improvements:
- When someone sends me a message, the notification doesn't use their avatar which keeps throwing me off:

- When first signing in, would be nice if it used my gpg to authenticate (if available) rather than asking for my passphrase. Especially since it has to do that later anyways.

:custard:

This is a metabug covering chat startup, invitations, unread counts, notification emoji and avatars, plus GPG-based sign-in. Start by reproducing the listed onboarding and notification experiences separately; done would require each reported behavior to have a confirmed fix or a separately tracked issue with clear ownership.

Written by the indexing model from the issue text.