Gate snapshot description and inline completions flags behind assistant config

[cstns]

Description

Important

This PR is part of a nested merge list, do not merge it until it's target is main

generatedSnapshotDescription and assistantInlineCompletions were previously hardcoded as true for all enterprise installations regardless of whether the assistant service was actually configured. This caused the features to appear available in the UI but fail at runtime on installations without assistant configuration.

Both flags are now derived from assistant.enabled === true && assistant.service.url being present, aligning them with how expertAssistant is already handled.

Related Issue(s)

closes #7311

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 76.59%. Comparing base (c1df27a) to head (f4ad728).

Additional details and impacted files

@@                               Coverage Diff                                @@
##           generic-ai-platform-and-team-level-feature-flag    #7318   +/-   ##
================================================================================
  Coverage                                            76.59%   76.59%           
================================================================================
  Files                                                  405      405           
  Lines                                                20614    20615    +1     
  Branches                                              4992     4993    +1     
================================================================================
+ Hits                                                 15789    15790    +1     
  Misses                                                4825     4825           

Flag	Coverage Δ
backend	76.59% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.