Refactor Cypress tests and ListBox component to improve selector usage

[cstns]

Description

Intermittent E2E failures are occurring due to CSS transitions on the Listbox options component. Because of the 100ms transition duration, there is a brief window where multiple instances of the options panel exist in the DOM simultaneously. This is particularly problematic on broker pages, where tests rapidly toggle multiple select-box components that share identical values (e.g., "Yes/No" options).

Why it occurs mostly in CI:

• CI environments are often slower and more variable than local machines, effectively widening the timing window where a "closing" listbox still resides in the DOM
• since the options are "teleported" to the document body, panels from different listboxes become top-level siblings. This removes any natural parent container scoping, leading to selector collisions

I have hardened the Cypress selectors for the select-box and applied them to the teleported options panels. This ensures more specific targeting and prevents the test runner from interacting with a stale component during transitions.

Related Issue(s)

closes #6691

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
• Link to Changelog Entry PR, or note why one is not needed.

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 76.65%. Comparing base (392a993) to head (ef3731c).
⚠️ Report is 13 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6727   +/-   ##
=======================================
  Coverage   76.65%   76.65%           
=======================================
  Files         398      398           
  Lines       20108    20108           
  Branches     4844     4844           
=======================================
  Hits        15414    15414           
  Misses       4694     4694           

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