[R-Dson]

Resolves #24 (asset + URL-install verification happens with the next release trigger).

• `scripts/fork-standalone-package.mjs`: derives a self-contained `@r-dson/pi-standalone` package from the coding-agent build — the bundle already inlines every workspace package, so dependencies are coding-agent's non-workspace entries verbatim (public npmjs only; no curated list to maintain). Ships the same file set as the upstream npm package (`dist`, `docs`, `examples`, `CHANGELOG.md` — the CLI reads themes/export templates/assets package-relative at runtime; a bundle-only tarball would crash at startup, caught in review), minus the shrinkwrap. Packs to a stable `pi-fork.tgz`.
• Workflow attaches `pi-fork.tgz` to each release (`--clobber` for re-runs) and the notes carry the one-line installs.
• `scripts/install-fork.sh` (curl|sh): validates npm/curl, accepts `v`-prefixed versions, downloads the release tarball, `npm install -g --ignore-scripts`.

Install with zero configuration and zero GitHub auth:
```
npm install -g https://github.com/R-Dson/pi/releases/latest/download/pi-fork.tgz

or

curl -fsSL https://raw.githubusercontent.com/R-Dson/pi/main/scripts/install-fork.sh | sh
```
GitHub Packages stays as the secondary channel for library-style use of the individual `@r-dson/*` packages (PAT required there).

14/14 script tests; `npm run check` clean.

This PR description is AI-generated.