Add Audio layout for apps (dotcom-rendering)

[DanielCliftonGuardian]

• Update src/layouts/DecideLayout.tsx to route Audio design to an Apps-compatible layout instead of falling through to StandardLayout
  • Modify AudioLayout.tsx to support renderingTarget: 'Apps' - remove NAV dependency, web-only ads, and header components for apps context
  • Create stories for Audio articles with renderingTarget: 'Apps'