Ensure that only Solid specific skills are in this repo

[jeswr]

Some skills like https://github.com/solid/solid-llm-skills/blob/main/engineering/release-engineer.md are general engineering skills rather than being Solid specific. We should move these to a separate repository.

[jeswr]

Perhaps in the readme of this repo, we can point to other useful skills such as these ones and "awesome-claude-repo"