Replace outdated UI screens with recent assets

[janbrasna]

One-line summary

Static fallbacks for wider locales, and a fallback of a fallback of a fallback home show several C–suite epochs old UI representation.

Significant changes and points to review

Randomly picked some more fun and colorful assets that fit the space nicely, for a less boring, and more Kit feel to that. Please do suggest otherwise/better if you have anything else in mind.

Issue / Bugzilla link

mozilla/bedrock#16011

Testing

http://localhost:8000/eu/download/windows/
http://localhost:8000/da/?xv=basic

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.72%. Comparing base (95ef069) to head (621104a).
⚠️ Report is 57 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1652   +/-   ##
=======================================
  Coverage   87.72%   87.72%           
=======================================
  Files         161      161           
  Lines       11032    11032           
=======================================
  Hits         9678     9678           
  Misses       1354     1354           

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