fix: update Hermes agent icon to Nous Research logo (#3150)

The Hermes agent site now uses the Nous Research logo instead of the
old snake icon. Update our bundled asset to match.

Co-authored-by: spawn-bot <spawn-bot@openrouter.ai>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: 3 people