Add context7.json with project URL and public key

[korenmiklos]

This enables us to add/update bead docs and skills for LLMs on context7.com.

Before submitting, please confirm the following:

• I have read and understood the project's CONTRIBUTING.md file.
• I agree to dedicate my contribution to the public domain under the terms of the LICENSE file.

[e3krisztian]

Well, it would have helped if I would get more context on this MR, as I am not familiar with context7.

E.g. it took me some time to locate

https://context7.com/docs/howto/claiming-libraries

and understand what this MR will enable.

TBH, I am still not sure who this will help, and how - I guess it helps for tool writers, who use the bead meta-data. But who writes code against bead repo/metadata and why exactly? I would like to learn about the problems.

Also, you should be aware, that there is a huge set of unreleased changes at https://github.com/e3krisztian/bead/tree/next so until those are merged, I would prefer not much change - no fixes, no new features, etc. to prevent conflicts. As this is a new file for repo configuration, this would not cause any problem, so good to go.