[codex] Narrow public API surface

[nahiyankhan]

Summary

• narrow public facade exports for @anarchitecture/summon, @anarchitecture/summon-server, and @anarchitecture/summon-react to explicit allowlists
• move runtime APIs to public subpaths and copied implementation output under dist/_internal/*
• update repo-internal imports, public package assembly, API manifest checks, smoke imports, docs, and changeset

Validation

• pnpm install
• pnpm typecheck
• pnpm build
• pnpm check:public-packages
• pnpm test
• pnpm pack:dry-run
• node scripts/smoke-public-packages.mjs
• pnpm test:safety

Note: the public package smoke test required network access to install tarball dependencies from npmjs during local verification.