Fix [object Object] request descriptions after OpenAPI import

[gschier]

Summary

• normalize Postman/OpenAPI description objects via a dedicated importDescription() helper using explicit if branches
• apply the helper to both workspace and request descriptions in the Postman importer path used by OpenAPI imports
• add regression tests in Postman and OpenAPI importer suites to ensure operation descriptions are imported as plain text

Validation

• npm run test --workspace @yaak/importer-postman
• npm run test --workspace @yaak/importer-openapi

Feedback

• https://yaak.app/feedback/posts/unexpected-request-info-description-after-openapi-import