publish: noisy throw stub for @rainlanguage/orderbook before raindex rename merges

[thedavidmeister]

Tracked from review of #2526 (Rename OrderBook to Raindex).

After #2526 merges, the `@rainlanguage/orderbook` package is gone from the repo and will stop receiving updates. Pinned consumers keep working, but anyone running `npm install` against an unpinned dep or auto-updates won't discover the rename.

Goal

Publish one final `@rainlanguage/orderbook@0.0.1-alpha.239` (or whatever's next) that throws at import time with the new package name in the error message. Forces consumers to migrate explicitly; no silent broken state.

Stub content

`packages/orderbook/dist/cjs/index.js` (and esm) replaced with:

```js
throw new Error(
'@rainlanguage/orderbook has been renamed to @rainlanguage/raindex. ' +
'Update your package.json and imports: ' +
'#2526'
);
```

The TypeScript declarations (`*.d.ts`) should be replaced with an empty module so type-check failures are immediate at the import site too.

Order of operations

1. Publish the stub from `main` (where `packages/orderbook/` still exists). Bump version, publish, confirm on npm.
2. Then merge Rename OrderBook to Raindex #2526. The rename PR removes the package directory; the npm record stays with the stub as the last published version.

If #2526 lands first the stub publish has to be reconstructed from history — doable but more friction.

Out of scope

Any version range or compatibility shim that lets old consumers keep importing without changes. We want a hard break with a clear message.

🤖 Generated with Claude Code

[linear]

RAI-620

[thedavidmeister]

Decided against — pinned consumers of @rainlanguage/orderbook keep working with their existing version, and forcing a hard break adds maintenance burden without enough benefit. Anyone hitting a 404 on a future install will find the new package easily via search.