build: yarn to bun

[mastercactapus]

Description:
This PR switches from using yarn and Node.js to using bun for all package management and JavaScript execution when building/testing UI code. With corepack potentially going away and various historical issues with versions of Node.js causing build breakage, this PR will use the gettool devtool to pull in the proper version of bun in the same way we do for tools like sqlc.

This eliminates the project's dependency on having the correct version of Node.js and simplifies the build process. Many of the workarounds for yarn pnp can all be cleaned up as bun uses the standard node_modules, but with speed and efficiency similar to (and faster than, in some cases) yarn pnp. This speed was the primary reason we switched to yarn, so this change seemingly solves the whole set of problems we've faced in the past.

This PR does not replace the use of esbuild, although bun may be able to replace that functionality too in the future. For now, that piece is out of scope.

Which issue(s) this PR fixes:
No associated issue.

Out of Scope:
The replacement of esbuild functionality is out of scope for this PR.

Additional Info:

• The main blocker is that dependabot doesn't yet support it add support for bun dependabot/dependabot-core#6528 (though renovate does, apparently)