[FEATURE]:

- [x] I have searched the existing issues to make sure this feature has not already been requested.

Similar but not quite the same ask: https://github.com/a2ui-project/a2ui/issues/2372

## Is your feature request related to a problem? Please describe.

`@a2ui/react` narrowed its [React peer dependency](https://github.com/a2ui-project/a2ui/blob/main/renderers/react/package.json#L124) to `^19.2.7` in a patch release, which has left our team pinned to `0.10.0`. It's also interesting that
1. it's specifically `>= 19.2.7`, which means it also excludes anyone on React 19.0 or 19.1
2. it landed in a patch bump, we can't upgrade to `0.10.1` because of this peer dependency

Our problem is that when future versions of `a2ui/react` support the new [v1.0](https://a2ui.org/specification/v1.0-a2ui/#the-readwrite-contract) schema, we won't be able to upgrade because of this peer dependency.

## Describe the Proposed Solution

Possible solutions that would help unblock our team from moving to `v1.0` schema:

1. Widen the peer range back to `^18.0.0 || ^19.0.0` if no React 19 only APIs are actually
required.
2. If React 19 only APIs are genuinely required, state the policy and maintain a React 18
compatible line that reaches schema v1.0. Even a 0.10.x style branch carrying `v1.0` entry
points would let consumers adopt the protocol on their own framework timeline.

## Describe Alternatives Considered
- `--legacy-peer-deps` / ignoring the peer warning. We won't do this. React 19 only APIs would fail at
runtime.
- Forking `@a2ui/react` to patch peerDependencies. We won't do this. This is an ongoing cost and maintenance burden for the team.
- Accelerating our own React 19 migration. As a large codebase, this is difficult as many products do not support v18 at the moment. There is no definitive timeline for when teams would move to v19.