Slate V2 Doc Convention Cleanup

Goal

Clean only the changed slate-v2 markdown files that picked up internal release-program language. Keep durable user-facing facts. Cut audit-style and verdict-style noise.

Scope

• root Readme.md
• changed walkthrough and concept docs where real guidance was added
• changed package/library readmes
• changed contributor docs only where internal test-program language leaked in

Keep

• headless installation and composition guidance
• current operations/history collaboration boundary facts
• current normalization behavior, written as product docs instead of status bookkeeping
• package usage summaries when they help users

Cut

• POC RC, True Slate RC, Target A, Target B
• proof-lane / verdict / roadmap accounting
• “replacement stack” framing in user-facing docs
• noisy internal performance or closure language