feat: add structured Swift errors

[biw]

Summary

• add opt-in SwiftNodeStructuredError with code, message, and JSON-safe details
• preserve ordinary Swift errors as normal JavaScript Errors while attaching structured properties across sync, async, and stream bridges
• export matching TypeScript error types, document the API, and bump the paired release packages to 0.1.5

Validation

• pnpm exec vp test run test/production-bridge.test.mjs
• pnpm --filter swift-node test -- generator.test.ts
• vp check
• pnpm check:package-versions
• pnpm precommit