DESIGN.md, CLAUDE.md, AGENTS.md: New file family gives AI agents persistent context

A new family of plain-text files—DESIGN.md, CLAUDE.md, and AGENTS.md—provides AI coding agents with persistent, repo-resident context for code, design, and project conventions. Each file handles a distinct concern, allowing teams to adopt them independently as needs arise. The pattern keeps agent-generated output on-brand and consistent without overlapping responsibilities.