fix(react): surface local tool responses

[osasisorae]

Summary

• ensure locally generated tool_response / tool_error messages are appended to the message stream and tool-status store so observers (onMessage, useVoice().messages, toolStatusStore) stay in sync even when EVI doesn’t echo custom tool replies
• extend the VoiceProvider test suite to cover the new behavior while keeping the existing ready-state sanity check

Testing

• pnpm --filter @humeai/voice-react test

Closes #388

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