chore: Add the Ristreto color to the palette

[g123k]

Hi everyone,

The Ristreto color is in the palette, even if we use it very rarely.
The main scenario is for the dark mode.

(Yes, I know, there is a typo on "Ristreto", but that's how it's written on Figma)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 7.37%. Comparing base (4d9c7fc) to head (bf66537).
Report is 191 commits behind head on develop.

Files	Patch %	Lines
...ges/smooth_app/lib/themes/smooth_theme_colors.dart	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           develop   #5379      +/-   ##
==========================================
- Coverage     9.54%   7.37%   -2.18%     
==========================================
  Files          325     384      +59     
  Lines        16411   19640    +3229     
==========================================
- Hits          1567    1449     -118     
- Misses       14844   18191    +3347     

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[teolemon]

☕