Dark mode additions vol 2

[jacbn]

Fixes the remaining documented issues with dark mode.

If any additional dark mode failures are found during testing, we probably ought to fix them here this time – but this by no means is required to be the last set of dark mode changes.

[codecov]

Codecov Report

❌ Patch coverage is 58.33333% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 43.55%. Comparing base (7f39265) to head (c79ce2a).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/app/services/constants.ts	0.00%	3 Missing ⚠️
...mponents/navigation/ResearchNotificationBanner.tsx	0.00%	1 Missing ⚠️
src/app/components/pages/GameboardBuilder.tsx	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #2207    +/-   ##
========================================
  Coverage   43.54%   43.55%            
========================================
  Files         597      597            
  Lines       25216    25223     +7     
  Branches     7477     8381   +904     
========================================
+ Hits        10980    10985     +5     
+ Misses      14187    14181     -6     
- Partials       49       57     +8     

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[axlewin]

Nice, I think this is pretty much ready to un-feature-flag 👍

A few minor outstanding issues I came across while testing:

• The (i) icon on the email verification banner isn't visible
• The contrast of the red 'Overdue' text on dashboard assignment cards is too low
• On the markbook, the colour code box for "Not attempted" still blends in with the background (I realise this isn't straightforward to fix by just editing the colour, but it looks a bit odd; maybe a border around the box like we have in light mode would work?)

Otherwise I think this is good to merge.