Create a 'Quick Start' guide

[4444J99]

Newcomers couldn't figure out which repository to clone first or how to run things locally. We need a clear entry point.

[4444J99]

Engagement disposition: distilled: QUICK_START.md. Main has a dedicated Quick Start that answers which repository to clone first, how to run checks for this governance repo, how to run public-process locally, the general clone/install/test pattern, and how first contributions should begin.