Scaffold Docs

Install the structure, not the content. Empty indexes are correct on day one — the wrap-up skill fills them in over time.

Only the first link in the chain is always in context:

CLAUDE.md → AGENTS.md (<50 lines, always loaded)
              ├→ docs/CONVENTIONS.md → docs/conventions/*.md  (hook surfaces these on edit)
              ├→ docs/INDEX.md       → docs/subsystems/*.md, docs/guides/*.md
              └→ docs/ARCHITECTURE.md

.github/instructions/conventions.instructions.md  (Copilot's entry to the same chain)
              └→ docs/CONVENTIONS.md

Every step merges. Never clobber a file that has content.