Notifications and emails showed the acting user's auto-generated
username instead of their display Name.
The doer attached to notification events was built straight from the
JWT via user.GetFromAuth, which only carries id + username (Name is
never set in GetUserFromClaims). Notifications render n.Doer.GetName(),
which falls back to the username when Name is empty, so every "assigned
you", "mentioned you", task-deleted, project-created and team-member
notification rendered the username.
Resolve the full user from the database at the event-producing dispatch
sites. doerFromAuth now re-fetches the user (with Name) and is reused by
all the notification doers; account-status errors are swallowed so flows
acting on behalf of disabled accounts (e.g. user deletion deleting that
user's tasks) keep working while still carrying the display name.
Fixes#2720
kolaente