add nix flake & add main-fn

[das-monki]

Adds a nix flake so the mcp-server can be run directly with nix run github:bhauman/clojure-mcp.

[das-monki]

@bhauman what do you think about this PR?

It makes it easy to set up if you don't intend to hack on it.

[bhauman]

Hey I really appreciate the intention, however

• software is very alpha, I'm trying not to "bless this as a working tool" until it gets into some kinda beta stage
• if we add a CLI I'd like it to be in its own namespace so that folks can require it into their custom main.clj file, I'd like the cli to be flexible enough that it doesn't need to be updated all the time as things change in this early period, hence my preference for -X which is very flexible takes whatever people pass into it. Whereas the CLI is a bottle neck that constricts expression and everything needs to be forced through it.

That being said I do want to facilitate folks experiencing the workflow, but I guess right now my focus is getting the tools to work better, solve the numerous alpha edge cases and I'm really not sure the maintenance of a flake is something I want to take on.

You know, I'm looking at this response, and I can't help but worry that I'm not a very good OS maintainer. I find it hard to let go of control and my own conceptions... yet I do want folks to contribute but I really haven't been successful at this.