Chore: Cleaning up package.json at root dir. Guiding users to package specific package.json

[TZubiri]

Issue for this PR

I didn't make a Github issue for each of the issues fixed, but each commit in this PR is an issue, here's a small recap, just in case:

1. Leftover boilerplate scripts
2. Message isn't clear, I thought it was about root user, not root dir.
3. Adding information about where to run the tests, not just where not to run them.
4. Adding information to bunfig.toml so that it affects 'bun test' as well. (hacky)

Added them as issue #18640 (Closes #18640)

Type of change

• Developer Experience
• Documentation (Kinda)

Small intro PR that I made while working on another more technical PR, to get warmed up.

What does this PR do?

The package.json file is usually what new devs look at when getting started analyzing the code.

There were 4 small issues with it, each with its own commit which you can inspect individually.

The broader picture is that new devs will find a (marginally) more polished Developer Experience.

How did you verify your code works?

Ran the affected bun and npm commands:

npm test
bun test
bun run dev

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

Hey! Your PR title Cleaning up package.json at root dir. Guiding users to package specific package.json doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍