Infrastructure: Split docs into ui.w3-kit.com when large enough

[PetarStoev02]

Parent

Part of w3-kit/cli#4 (Phase 5: Scale + Community)

Goal

When the UI component library grows large enough, split it into its own subdomain.

Trigger

• Component count reaches ~30-40
• docs.w3-kit.com becomes hard to navigate with all content

Requirements

• Dedicated UI component documentation site at ui.w3-kit.com
• Component playground / live preview
• Search across components
• Keep docs.w3-kit.com for guides and recipes