refactor: split generated output into individual files per enum/resource

[joshmanders]

Summary

• Split bundled index.d.ts / index.js output into individual files per enum and resource (e.g., StatusEnum.d.ts, UserResource.d.ts)
• Added barrel export files (index.d.ts, index.js) that re-export all types for backwards-compatible imports
• Added cleanOutputDir() helper to remove stale generated files when enums/resources are deleted
• Individual resource files now only import the specific enums they reference

New Output Structure

node_modules/@ferry/enums/
├── StatusEnum.d.ts
├── StatusEnum.js
├── index.d.ts       # export { StatusEnum } from './StatusEnum.js';
└── index.js

node_modules/@ferry/resources/
├── UserResource.d.ts
├── UserResource.js
├── index.d.ts       # export type { UserResource } from './UserResource.js';
└── index.js

Test Plan

• All existing tests pass
• Build succeeds with no TypeScript errors