feat(huh): match huh to legacy styling

[srtaalej]

Changelog

na

Summary

• Add ThemeSurvey() huh theme that replicates the legacy survey prompt appearance (gray+bold titles, blue+bold cursors/chevrons, [x]/[ ] multi-select prefixes, red errors) so huh forms look identical to survey when only experiment.Huh is on without experiment.Lipgloss
• Apply ThemeSurvey() as default in newForm() — ThemeSlack() is used when Lipgloss is on, ThemeSurvey() otherwise
• Style select option descriptions with bold option name + gray description text (via style.Bright/style.Secondary) and em-dash separator consistently across both experiment paths

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.