Add hero card polymiddleware infrastructure

[Claude]

Implements hero card polymiddleware to enable customization of hero card rendering, following the existing activity and error box polymiddleware patterns.

Changes

• Created heroCardPolymiddleware.tsx in api-middleware package

  • Request type: { readonly heroCard: unknown } with no props
  • Exports createHeroCardPolymiddleware, HeroCardPolymiddlewareProxy, heroCardComponent, and related types

• Integrated into PolymiddlewareComposer

  • Added HeroCardPolymiddlewareProvider to provider chain
  • Extracts and applies hero card enhancers alongside activity and error box polymiddleware

• Refactored HeroCardAttachment

  • Converted from .js to .tsx with TypeScript types and valibot validation
  • Replaced direct rendering with HeroCardPolymiddlewareProxy

• Added default implementation

  • Created createDefaultHeroCardPolymiddleware() that renders existing HeroCardContent component
  • Wired into bundle via useComposerProps polymiddleware array

• Exported from all middleware entry points

  • packages/api-middleware/src/index.ts
  • packages/api/src/boot/middleware.ts
  • packages/bundle/src/boot/actual/middleware.ts

Usage

// Custom hero card rendering
const customHeroCardMiddleware = createHeroCardPolymiddleware(
  () => ({ heroCard }) => heroCardComponent(MyCustomHeroCard, { content: heroCard })
);

<Composer polymiddleware={[customHeroCardMiddleware]}>
  {/* Hero cards will now use custom renderer */}
</Composer>