fix: rebuild game-bridge with Chrome 60 target for better WebView compatibility

CRITICAL ROOT CAUSE FOUND:
game-bridge was failing with:
  SyntaxError: Unexpected token '.'. Expected a ';' following a class field.

This is caused by ES2022 private class fields (#field) that old WebView doesn't support.

SOLUTION:
1. Changed Parcel target from Chrome 90 -> Chrome 60 in package.json
2. Added Babel plugins for class properties and private methods transformation
3. Set @babel/preset-env target to Chrome 60
4. Rebuilt game-bridge - size increased from 1.83MB to 1.88MB (more transpilation)

Chrome 60 target ensures compatibility with old CEF/WebView engines used by Unity.

Next test run should finally work with properly transpiled JavaScript.

Author: rodrigo-fournier-immutable