fix(*): externalize dependencies and add rollup-plugin-visualizer [KHCP-5862]

[adamdehaven]

Summary

Our packages were not properly listing build.rollupOptions.external in the vite.config.ts to prevent certain imports/dependencies from being bundled, meaning the bundle sizes were 1-2 MB (😱).

I have added an entry in the shared config at the root of the repo. Any externals added at the package level will be merged with the root config array.

PR Checklist

• Naming & Structure: the files and package structure use the conventions outlined in the Creating a Package docs.
• Tests pass: check the output of all package unit and/or component tests.
  • If this PR is the result of a bug, test coverage was added accordingly.
• Functional: all changes do not break existing APIs, but if so, a BREAKING CHANGE commit is in place to bump the major version.
• Conventional Commits all commits follow the conventional commit standards outlined in the main README.
• Docs: includes a technically accurate README, and the docs have been updated accordingly based on the changes in this PR.