refactor(react)!: adopt Effect Atom lifecycle state (#46)

## Summary

- make the canonical `domainkit` `Transport` service the only React wire
contract
- run connection, provisioning, cleanup, verification, and disconnect
controllers through Effect Atom
- expose `Connection.useModel(domain)` plus typed `Connection.Command`
constructors so custom Effect UI consumes the same atoms as the packaged
controller and flow
- accept a `Layer<Transport.Service>` at `DomainKit.Root`, with
`Transport.layerFromAsync` for Promise hosts
- require React 19 and remove the React-owned transport and request
identity implementations
- update docs, testing utilities, packed consumers, and release metadata
for the 0.3 contract

## Verification

- `bun run release:check`
- `bun run docs:build`
- `bun run docs:audit`

## Breaking changes

`DomainKit.Root` now accepts a `Layer<Transport.Service>`, React-owned
`Transport` exports are removed, controller actions dispatch
synchronously through Effect Atom, and React 18 is no longer supported.