While I do think it's easy (and justified) to be a little full of righteous indignation over this, I do think in general people (myself included, but not necessarily this author) tend to overvalue their code. It's an expression of our imagination and skills, and is our little baby, so it makes a lot of sense that we would ascribe higher value to it than someone else might, but I think the occasional re-grounding is healthy. Code in and of itself isn't usually very valuable, in fact it is often worthless. (Note I'm not saying Enigo is worthless, in fact it's clearly far from it, but the vast, vast majority of open source code does tend to be relatively worthless. Do a github search for various things if you don't believe me). Remembering this (at least for me) reduces the sting a little bit.
Now that said, I think there's an opportunity here for you. It's rare, but I've known people who spun open source like this into a revenue source, not directly from the company but from other ways. My advice (if you have the time/motivation/willingness): Embrace Anthropic's use here, even maybe reach out and help accomodate them for features! Offer to help get the Linux build working (you would be a personal hero of mine for that!). They may even hire you once they see that you're genuinely good and helpful. I have seen many times in the past (including personal experience) trying to hire an open source dev, and we discovered that they weren't actually very nice people, and in about half the cases they were outright arrogant, possibly even with a superiority complex. The beautiful thing about code is that it doesn't care about personalities, but rather "does it work." In a workplace though, personalities are (often) even more important than code. We almost hired one of the most brilliant open source guys I've ever seen - his code was like a work of art, and his domain knowledge was unparalleled. But he was an asshole to the HR person, was openly critical of our interview process (during the interview!), and had virtually no tact when talking to what would be his fellow coworkers. It's ok (and sometimes very good) to correct an interviewer if they ask or say something technically incorrect, but the way you do that matters. Don't immediately retort with stuff like "that's completely and utterly wrong" or "that's a really stupid way to solve that." Nobody wants to work with people like that. Of course I'm not suggesting that OP is that way, but rather trying to share some personal experience as to why a company may not be in a rush to hire an open source contributor. To be clear, that doesn't justify what they've done, but I do think remembering that Anthropic isn't just a giant monolith, but is rather made up of other humans that are just as human as we all are can be very helpful at understanding why things sometimes go the way they do.
On the license question, I'm a huge proponent of the GPL/AGPL (I would always suggest licensing end-user software this way), but I think for libraries like this MIT is usually the best option. Had you licensed it AGPL it may never have gotten traction in the first place, and you'd be worse off than you are now. It's possible it could have led to licensing, but having seen the inner-workings of big tech companies, I highly doubt it.
Apologies for the length of this. It struck a chord with me because I've had libraries used in a similar way (though at a much smaller scale) and had to do a lot of soul searching on it.
Regardless, awesome work! At a minimum you now have an awesome story to tell and you're part of a small club of people that have been successful enough to get hit :-D