fix(react): support SSR for A2uiSurface

[gaoachao]

Description

Close #2080.

A2uiSurface could not render in an SSR environment because the React v0.9 calls to useSyncExternalStore did not provide getServerSnapshot. React requires this callback during server rendering and threw a Missing getServerSnapshot error before hydration.

This change uses each store's existing stable snapshot getter as its server snapshot provider in both A2uiSurface and the component binding adapter.

The added tests verify that:

• A populated surface renders to HTML on the server.
• The client hydrates the server output without recoverable errors.
• Data model updates remain reactive after hydration.

There are no visual or public API changes.

Pre-launch Checklist

One time:

• I signed the CLA.
• I read the Contributors Guide.
• I read the Style Guide.
• I have built and run at least one sample.

For this PR:

• I have updated the relevant CHANGELOG.md file.
• No documentation update is needed because this change does not modify the public API or usage.
• My code changes have tests.
• If my branch is on a fork, I have verified that scripts/e2e_test.sh passes.

If you need help, consider asking for advice on the discussion board.

[gemini-code-assist]

Code Review

This pull request introduces support for server-side rendering (SSR) and hydration in the React renderer by passing the third argument (getServerSnapshot) to useSyncExternalStore in both A2uiSurface and the component adapter. Additionally, a new test suite has been added to verify SSR rendering and hydration, and the changelog has been updated. I have no feedback to provide.

[Varun-S10]

@gaoachao, could you please update your PR branch with the latest changes from the base branch (main)? Once updated, the PR will be reviewed. Thank you for your patience and understanding.

[gaoachao]

@Varun-S10 Thanks! I've updated the branch with the latest changes from main. It's ready for review now.

[Varun-S10]

Hi @gaoachao, I have reviewed and verified the changes. Thank you for your contribution.

Hi @ditman, I would like to escalate this PR. Could you please take a look?

[ditman]

This look great! @gaoachao how are you using A2UI with React SSR? Do you have anything server-specific, or are you using the standard stack? Can you show a demo maybe with hardcoded JSON or similar?