- New isValidPhone(raw): checks 11-digit Russian after normalization (8/7/+7/9-prefix)
- Intro 'Начать' button now custom click handler instead of data-go
- Validates name (non-empty) and phone (Russian format)
- Inline .field-error red message under invalid field
- .field-hint shows format help under phone input
- Haptic 'warning' feedback on invalid submit
- Phone is auto-normalized to '+7 900 123-45-67' before transition
