Check in lockfile and use npm consistently

[chaance]

Description

We should be checking in the lockfile to ensure dependencies are consistent across environments. Since we use npm in CI it seems to make sense that we use it on the development side as well.

Documentation

Does this require changes to the WorkOS Docs? E.g. the API Reference or code snippets need updates.

[ ] Yes

If yes, link a related docs PR and add a docs maintainer as a reviewer. Their approval is required.

[greptile-apps]

Greptile Summary

This PR standardizes the project's package management by migrating from Yarn to npm across all environments. The changes include:

• Package management migration: Updates package.json to use npm run build instead of yarn run build in the prepublishOnly script
• Lockfile strategy change: Removes package-lock.json from .gitignore and adds yarn.lock to it, ensuring npm's lockfile is tracked in version control for consistent dependency resolution
• Build script updates: Modifies bin/restore-or-install to use npm commands (npm install and npm ci) instead of yarn, while maintaining the same caching logic based on package-lock.json checksum
• Documentation alignment: Updates installation instructions in README.md from yarn add @workos-inc/node to npm i @workos-inc/node

The migration addresses environment consistency since the CI pipeline already uses npm. By checking in the lockfile, the project ensures deterministic dependency resolution across development, CI, and production environments. This eliminates potential "works on my machine" issues caused by different package managers resolving dependencies differently. The changes maintain existing functionality while standardizing the toolchain.

Confidence score: 4/5

• This PR is generally safe to merge with proper coordination across the development team
• Score reflects solid technical changes but requires team coordination to ensure all developers switch from yarn to npm
• Pay close attention to the bin/restore-or-install script logic with npm ci usage

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[greptile-apps]

logic: Using npm ci here may cause issues since it removes existing node_modules before installing. If the first condition already installed dependencies, this will unnecessarily reinstall everything. Consider using npm install or checking if this condition is actually needed.

Suggested change

	npm ci
	npm install