ui: overview page fixes (PROJQUAY-7107)

[dmesser]

This fixes a range of smaller issues with the overview page:

• Dark Mode is not supported well (some black text on dark background)
• Incorrect links directly to Quay.io, which leave the Cloud Console
• lack of vertical padding in the pricing tab
• some language on the call to actions
• low res screenshot of Quay UI (now also alternating depending dark/light theme selection)

[dmesser]

The Cypress test is failing because the default security policies probably prevent us from writing into the clipboard in Chrome at CI runtime. This is addressed in #2840

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.92%. Comparing base (4bfad98) to head (b1411cc).
Report is 7 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2843      +/-   ##
==========================================
- Coverage   70.93%   70.92%   -0.01%     
==========================================
  Files         436      436              
  Lines       40723    40735      +12     
  Branches     5323     5328       +5     
==========================================
+ Hits        28887    28892       +5     
- Misses      10152    10157       +5     
- Partials     1684     1686       +2     

Flag	Coverage Δ
unit	70.92% <ø> (-0.01%)	⬇️

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[bcaton85]

LGTM