test(release): prove aligned Effect-first packages (#49)

## Summary

- align `domainkit` and `@domainkit/react` on Effect 4 RC.112 and expose
Effect Atom as a React peer so consumers share one runtime
- prove host-composed Atom usage and the packaged `Domain.Flow` recipe
against the same packed transport/model contract
- coordinate future public-package bump types and align the next release
preview at `domainkit@0.3.0` and `@domainkit/react@0.3.0`
- document the complete React 19 / Effect / Effect Atom installation
contract

`@domainkit/react` is currently published at `0.1.1`, while `domainkit`
is at `0.2.2`. Its manifest baseline moves to the unpublished `0.2.2`
line so the next coordinated minor release is `0.3.0` for both packages;
this PR does not publish either package.

## Consumer contract

```sh
npm install domainkit effect@rc
npm install @domainkit/react domainkit effect@rc @effect/atom-react@rc react react-dom
```

The packed Vite consumer renders the packaged recipe beside a custom
component that calls `Connection.useModel`, reads its state with
`useAtomValue`, and dispatches `Connection.Command.Retry()` with
`useAtomSet`.

## Verification

- `bun run release:check`
- core: 26 files / 132 tests, packed Node 24, Bun, and workerd consumers
- React: 7 files / 50 tests, packed Vite and Next consumers, 7
Playwright tests
- `bun run --cwd apps/docs registry:check`
- `bun run docs:build`
- `bun run docs:audit` — 1,064 audits, 0 errors, 0 warnings, 0 notes
- `git diff --check`