🗜️ fix react and react-native versions

[JGreenlee]

react-native 0.78.0 is out now, which uses React 19, but we are still using React 18, causing npm to complain about incompatible versions. Locking down the react-native version to 0.76.7 allows us to stay on React 18 for now.
We do want to go to React 19 eventually, so I am changing React libs to ^18.2.0. This allows 18.3.0 to be used which will give us warnings in the console if we use any deprecated features that won't work in React 19 https://react.dev/blog/2024/04/25/react-19-upgrade-guide#react-18-3

Note that we don't even use the react-native package itself; we just use react-native-web. react-native gets downloaded anyway because it's listed as a peer dependency of @react-navigation/native which we do use.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 29.76%. Comparing base (cce8b91) to head (f31f542).
Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1200   +/-   ##
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  Coverage   29.76%   29.76%           
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  Files         123      123           
  Lines        4959     4959           
  Branches     1096     1143   +47     
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  Hits         1476     1476           
  Misses       3483     3483           

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