Add a three-layer page component system for realistic BrowserView
content:

- Layer 1 (primitives): PageLayout, AppBar, SideNav, FormCard,
  DataTable, SettingsForm, Breadcrumb, StatusBadge — composable
  building blocks using Tailwind and --scenar-* theme tokens
- Layer 2 (templates): LoginCardPage, SettingsFormPage,
  AdminListPage, DashboardPage — pre-composed page layouts for
  common scenario patterns (login, settings, admin, dashboard)

TerminalView improvements:
- Increase padding (px-3 → px-5, py-2 → py-3) for better content
  distribution across the viewport width
- Bump default font size from 11px to 13px with configurable
  fontSize prop
- Increase line height to 1.7 for readability
- Widen prompt element spacing for breathing room

All new components are exported from the @scenar/react public API.

Made-with: Cursor