Fix Railway build by removing @clerk/shared/types import

[codybmenefee]

Summary

• replace @clerk/shared/types import in useResolvedBillingAccess with local structural billing types
• keep behavior unchanged while avoiding module resolution failure in CI
• preserve strict typing for subscription item/plan/feature traversal

Why

Railway build environment could not resolve @clerk/shared/types, causing TS2307 and cascading implicit-any errors.

Validation

• cd app && npx eslint src/lib/auth/useResolvedBillingAccess.ts
• cd app && pnpm run build