Add json input support for script arguments

[BlakeASmith]

Add support for passing arguments via JSON input to Argorator CLI, allowing users to define parameters as a JSON object.

This feature introduces a --json-input option to accept a JSON string or read from stdin, and also automatically consumes JSON from stdin if no other arguments are provided and stdin is not a TTY. Scripts can opt out of this functionality using an argorator: no-json-input directive comment.

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[cursor]

Cursor Agent can help with this pull request. Just @cursor in comments and I'll start working on changes in this branch.
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