Description of changes

Resolves #6432

Adds Amazon Bedrock Guardrails support to the AIConversation component and createAIConversation factory in the @aws-amplify/ui-react-ai package.

Guardrails enforce safety policies (content filtering, denied topics, sensitive information redaction, etc.) on AI model responses via the Bedrock Converse API. This was previously unavailable in the UI kit despite the underlying API supporting it natively.

Usage:

// Via factory
const { AIConversation } = createAIConversation({
  guardrails: {
    guardrailIdentifier: 'abc123xyz',  // from AWS Bedrock console
    guardrailVersion: '1',             // or 'DRAFT'
    trace: 'enabled',                  // optional
  },
});

// Or directly on the component
<AIConversation
  guardrails={{ guardrailIdentifier: 'abc123xyz', guardrailVersion: '1' }}
  messages={messages}
  handleSendMessage={handleSendMessage}
/>

Implementation notes:

• Guardrails are conversation-level (not per-message), consistent with allowAttachments and responseComponents
• Follows the same pattern as the existing AIContextContext / toolConfiguration feature
• New GuardrailConfiguration type is publicly exported from @aws-amplify/ui-react-ai
• @aws-amplify/data-schema's ConversationSendMessageInputObject does not yet include guardrailConfiguration — a type cast is used internally (safe since Bedrock already supports the field natively). A companion issue in aws-amplify/amplify-data should add the upstream type so the cast can be removed.

Issue #, if available

Closes #6432

Description of how you validated changes

• Added 4 new unit tests for GuardrailsContext (default value, config passthrough, trace mode, undefined passthrough)
• Added 2 new unit tests in FormControl.spec.tsx (message sent without guardrails, message sent with guardrails)

Checklist

• Have read the Pull Request Guidelines
• PR description included
• yarn test passes and tests are updated/added
• PR title and commit messages follow conventional commit syntax
• If this change should result in a version bump, changeset added (minor bump for @aws-amplify/ui-react-ai)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.