Fix limbo state after leaving last team

[Steve-Mcl]

closes #4026

Description

• Awaits teams refresh
• checks team count, if zero, sets own team to null
  • this causes links in sidebar to correctly change from "back to dashboard" to "back to create team"

Before

After

Related Issue(s)

#4026

Checklist

• I have read the contribution guidelines
• Suitable unit/system level tests have been added and they pass
• Documentation has been updated
  • Upgrade instructions
  • Configuration details
  • Concepts
• Changes flowforge.yml?
  • Issue/PR raised on FlowFuse/helm to update ConfigMap Template
  • Issue/PR raised on FlowFuse/CloudProject to update values for Staging/Production

Labels

• Includes a DB migration? -> add the area:migration label

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.64%. Comparing base (940a813) to head (84f6bac).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4226   +/-   ##
=======================================
  Coverage   78.64%   78.64%           
=======================================
  Files         286      286           
  Lines       13119    13119           
  Branches     2934     2934           
=======================================
  Hits        10317    10317           
  Misses       2802     2802           

Flag	Coverage Δ
backend	78.64% <ø> (ø)

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