Feat: Spinner, JS API, check files

[gaurav-nelson]

• Separated CLI app code and created a JS library. This is preparation to create a GitHub action for linkspector.
• Added spinner animation when the check is in progress.
• Updated the check function to process filenames, handles the case when filenames are used instead of hyperlinks.

[gaurav-nelson]

Fix validation error as well in this PR:

⠋ Validation Error [
  {
    message: "\"dir\" is not allowed",
    path: [ "dir" ],
    type: "object.unknown",
    context: {
      child: "dir",
      label: "dir",
      value: [ null ],
      key: "dir"
    }
  }
]
✨ Success: All hyperlinks in the specified files are valid.