Add collaborative to demo

[bollwyvl]

• [x] add collaborative: true
• [x] rework extension fixturing
• [x] make a room ui for docs

[codecov[bot]]

Codecov Report

Merging #64 (5ea5fc9) into master (0a80d24) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #64   +/-   ##
=======================================
  Coverage   96.47%   96.47%           
=======================================
  Files          25       25           
  Lines         710      710           
  Branches       58       58           
=======================================
  Hits          685      685           
  Misses         13       13           
  Partials       12       12           

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