i3 Dockerise the app

[hillalex]

This PR adds:

• custom Express server file and npm tasks for compiling and runing the production build
• Dockerfile, build/push/smoke-test scripts
• GH action for building, testing and pushing the docker image
• some opportunistic fixes to the color logic

Closes #3

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (3b19d22) to head (7097e2b).

Additional details and impacted files

@@            Coverage Diff            @@
##              main        #9   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines           30        30           
  Branches         6         6           
=========================================
  Hits            30        30           

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