Fix ClientError native ESM import

[omribz156]

Summary

• add conditional package exports for @mondaydotcomorg/api
• route native Node ESM imports to an .mjs build output, while keeping the existing .js ESM bundle and CJS entry
• expose ./package.json through the exports map

Fixes #89.

Verification

• corepack yarn install --frozen-lockfile
• corepack yarn workspace @mondaydotcomorg/api build
• npx -y node@18 --input-type=module -e "import { ClientError } from '@mondaydotcomorg/api'; console.log(ClientError.name);"
• node --input-type=module -e "import { ClientError } from '@mondaydotcomorg/api'; console.log(ClientError.name);"
• node -e "const { ClientError } = require('@mondaydotcomorg/api'); console.log(ClientError.name);"
• corepack yarn workspace @mondaydotcomorg/api test --runInBand
• ./node_modules/.bin/prettier.cmd --check packages/api/package.json packages/api/rollup.config.js
• git diff --check -- packages/api/package.json packages/api/rollup.config.js

Implemented with Codex assistance; I kept the patch focused and manually verified the package-name import path that fails in the issue.