fix: Handle undefined text color

[iamareebjamal]

Fixes #4850

• Make helper handle temporary undefined values
• Load sessions and tracks in one go for featured speakers
• Filter speakers with deleted or unconfirmed sessions

[vercel]

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[codecov]

Codecov Report

Merging #4851 into development will increase coverage by 0.01%.
The diff coverage is 66.66%.

@@               Coverage Diff               @@
##           development    #4851      +/-   ##
===============================================
+ Coverage        23.29%   23.30%   +0.01%     
===============================================
  Files              480      480              
  Lines             5082     5084       +2     
  Branches            16       17       +1     
===============================================
+ Hits              1184     1185       +1     
  Misses            3895     3895              
- Partials             3        4       +1     

Impacted Files	Coverage Δ
app/routes/public/index.js	0.00% <ø> (ø)
app/helpers/text-color.ts	66.66% <66.66%> (-33.34%)	⬇️

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