refactor(ui): modernize code for eslint 10 and react best practices

[erka]

• Replace let with const for non-reassigned variables
• Remove unused catch parameters and function arguments
• Remove eslint-disable comments where violations are fixed
• Fix isFetchBaseQueryError return type to eliminate @ts-ignore
• Route navigation through browser.navigateTo abstraction
• Simplify SegmentsPicker: useMemo over useRef/useEffect
• Fix Analytics: derive selectedFlag and pollingInterval with useMemo
• Fix Preferences: useRef for isInitialLoad, streamline debounce

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 62.27%. Comparing base (2ba7835) to head (521b835).

Additional details and impacted files

@@           Coverage Diff           @@
##               v2    #6227   +/-   ##
=======================================
  Coverage   62.27%   62.27%           
=======================================
  Files         145      145           
  Lines       14815    14815           
=======================================
  Hits         9226     9226           
  Misses       4829     4829           
  Partials      760      760           

Flag	Coverage Δ
integrationtests	33.50% <ø> (ø)
unittests	53.85% <ø> (ø)

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

☔ View full report in Codecov by Harness.
📢 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.

[github-actions]

Verdict: approve

Clean mechanical refactor. The const/let fixes, unused-parameter cleanups, eslint-disable removals, type-guard correction, and effect simplifications in SegmentsPicker and Analytics all look correct. The prior automated review’s two concerns (Preferences.tsx missing a mount effect and NavUser.tsx duplicate import) appear to have been based on a misread—the current diff preserves the separate mount effect and has only a single merged import line. No changes requested.

🤖 Automated review by the Flipt PR review agent.