Move internal notes out of the public repo

[is2b007]

What changed

• removed the local-only AGENTS.md prompt from the public tree
• archived obsolete build-plan, editor-plan, launch-checklist, product-brief, and visual-reference notes outside Git
• retained the important product invariants in CONTRIBUTING.md
• removed stale pre-public wording and dead documentation links
• ignored local agent, Codex, and browser scratch files

Local archive

The removed material is preserved under:

~/Documents/Reed Local Archive/2026-07-22 repository cleanup/

The main checkout's 55 untracked duplicate, scratch, and case-study files were also moved there with their original directory layout.

Validation

• pnpm typecheck
• pnpm test:offline
• gitleaks git --no-banner
• no remaining references to removed documents
• archived tracked files verified byte-for-byte before removal