bug: Cannot add user+domain on server identities

Checks

[X] I have searched github.com/withfig/fig/issues and there are no duplicates of my issue
[X] I have run fig doctor in the affected terminal session
[X] I have run fig restart and replicated the issue again

Operating system

macOS 13.4.1 (22F770820d)

Expected behaviour

1. Go to Servers -> Identities -> New Identity -> type a user+domain like "myuser@mydomain.com" and fill nickname + authentication type -> Click Create -> the new identity is shown in the list

Go to Servers -> Identities -> New Identity -> type a user without domain like "myuser" and fill nickname + authentication type -> Click Create -> the new identity is shown in the list
Go to Servers -> Identities -> Edit Identity with a user without domain -> concatenate the domain to the user like "myuser@mydomain.com" -> Click Apply Changes -> the edited identity is shown in the list and the NEW username is visible in the list.

Actual behaviour

1. Go to Servers -> Identities -> New Identity -> type a user+domain like "myuser@mydomain.com" and fill nickname + authentication type -> Click Create -> the new identity is shown in the list for half of a second, and then it disappears

Go to Servers -> Identities -> New Identity -> type a user+domain like "myuser@mydomain.com" and fill nickname + authentication type -> Click Create -> the new identity is shown in the list and remains there.
Go to Servers -> Identities -> Edit Identity with a user without domain -> concatenate the domain to the user like "myuser@mydomain.com" -> Click Apply Changes -> the edited identity is shown in the list for half a second and then reverts to the version before edit.

Steps to reproduce

add a user without domain and add the domain later by editing the user

create a user with domain

Environment

fig-details:
  - 2.16.0
hardware-info:
  - model: 
  - model-id: 
  - chip-id: Apple M1 Max
  - cores: 10
  - mem: 32.00 GB
os-info:
  - macOS 13.4.1 (22F770820d)
environment:
  - shell: /Applications/Fig.app/Contents/MacOS/fig_desktop
  - terminal: terminal
  - cwd: /
  - exe-path: /Applications/Fig.app/Contents/MacOS/fig-darwin-universal
  - install-method: brew
  - env-vars:
    - FIG_TERM: 2.16.0
    - __CFBundleIdentifier: com.mschrage.fig
    - PATH: /opt/homebrew/sbin:/opt/homebrew/sbin:/usr/local/bin:/System/Cryptexes/App/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/Applications/VMware Fusion.app/Contents/Public:/Library/Apple/usr/bin:/Applications/Wireshark.app/Contents/MacOS:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/local/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/appleinternal/bin:/Users/mccasian/.fig/bin:/Users/mccasian/.local/bin:/opt/homebrew/bin/:/opt/homebrew/bin/
    - TERM: xterm-256color
    - FIG_SET_PARENT_CHECK: 1
    - FIG_SET_PARENT: c3a4c652-e6ac-4e3c-8c7c-cbde6dfbae90
    - FIG_PID: 50321
    - SHELL: /bin/zsh
    - FIGTERM_SESSION_ID: c3a4c652-e6ac-4e3c-8c7c-cbde6dfbae90

withfig / fig