Add a 'Customise' menu item to the variants dropdown in the chat box
that navigates users to the Agent Settings page (/settings/agents)
where they can configure executor variants.
- Add onCustomise callback to VariantProps interface in ChatBoxBase
- Render separator and Customise option with gear icon in dropdown
- Add navigation handler in SessionChatBoxContainer and CreateChatBoxContainer
- Add i18n translations for all supported locales
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>