fix: dark mode regressions

[HarishChandran3304]

PR to fix dark mode regression issues mentioned in #3358

Fixes:

1. Invisible dividers in Settings list views -> bump <hr> to --outline-gray-2 in dark mode only
2. Mobile sidebar washed the screen near-white -> use bg-black-overlay-500

Screen.Recording.2026-05-18.at.3.10.06.PM.mov

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.06%. Comparing base (ec40d5a) to head (962546b).
⚠️ Report is 3 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3366      +/-   ##
===========================================
- Coverage    59.07%   59.06%   -0.02%     
===========================================
  Files          129      129              
  Lines         6515     6515              
===========================================
- Hits          3849     3848       -1     
- Misses        2666     2667       +1     

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[RitvikSardana]

[HarishChandran3304]

@RitvikSardana will fix this by EOD