[Docs] We no longer use Slopwatch. Remove from agentic coding advice #4557

]Is your feature request related to a problem? Please describe.

We no longer use SlopWatch, it had different rules to us, and didn't cope with some older parts of our codebase: https://github.com/BrighterCommand/Brighter/blob/master/AGENTIC_CODING.md

Describe the solution you'd like
Remove references to SlopWatch from our docs

Describe alternatives you've considered
We could install our own hooks or configure SlopWatch better, but we are dubious of utility as models improve