Move demo pages to /public folder

[marlo-longley]

This removes the long URLs at __tests__/integration/mirador
This is possible because of the recent work to decouple the integration tests from these pages.
This also seems to fix some issues with HMR and reloading these pages using Vite's dev server; Vite prefers things to be in /public.
Now locally you would go to http://localhost:4444/collections.html, http://localhost:4444/index.html, etc.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.80%. Comparing base (1fb2797) to head (b14e791).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4119   +/-   ##
=======================================
  Coverage   94.80%   94.80%           
=======================================
  Files         323      323           
  Lines       16158    16158           
  Branches     2539     2541    +2     
=======================================
  Hits        15318    15318           
  Misses        835      835           
  Partials        5        5           

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