CLI: Fix getFrameworkPackage logic

[yannbf]

Relates to #18360

What I did

The CLI had a bug in the way it tried to detect a framework package. That caused the following issue:
Sorry, for now, you can not do this, please use a framework such as @storybook/react-webpack5

This PR fixes that bug, and also throws a descriptive error to assist users in case they hit this scenario

How to test

1. Go to a project without Storybook
2. Build the CLI and use it like so: storybook init --builder XYZ:
   a. --builder vite (should work)
   b. --builder @storybook/builder-vite (should work)
   c. --builder vitest (should throw an error telling you to check if the package exists)

Checklist

• Make sure your changes are tested (stories and/or unit, integration, or end-to-end tests)
• Make sure to add/update documentation regarding your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Maintainers

• If this PR should be tested against many or all sandboxes,
  make sure to add the ci:merged or ci:daily GH label to it.
• Make sure this PR contains one of the labels below.

["cleanup", "BREAKING CHANGE", "feature request", "bug", "documentation", "maintenance", "dependencies", "other"]