JavaScript/Node.js Language Toolchain

Sets up Node.js, package managers (bun, npm, pnpm, yarn), and auto-install hooks. This replaces devenv's languages.javascript module.

The auto-install feature (e.g., bun.install.enable) runs the package manager's install command on shell entry, but only when the lockfile has changed since the last install. This avoids redundant installs on every shell entry.

Usage in .stack/config.nix:

languages.javascript = {
  enable = true;
  bun.enable = true;
  bun.install.enable = true;
};