feat: add groups API to SDK

[ferreiro]

adding our new groups functionality that allows you to assign users to "groups", this is awesome for multi-tenant workspaces or "teams" to get insights at the "workspace" level

---

Note

Medium Risk
Introduces a new public SDK surface area and new endpoint wiring (including contact membership paths), which could cause breaking behavior if API paths/types are wrong; changes are otherwise additive and well-tested.

Overview
Adds a new Groups API client (smashsend.groups) with methods to create, list, get, update, and delete groups, plus endpoints to addContact, removeContact, and listContacts.

Exports new group-related TypeScript interfaces from index.ts and adds comprehensive Jest coverage for all group methods using a mocked HttpClient.

Also adds contacts.upsert() as a documented alias of contacts.create() for create-or-update-by-email flows.

^{Reviewed by Cursor Bugbot for commit 15af3d3. Bugbot is set up for automated code reviews on this repo. Configure here.}

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.}

^{Reviewed by Cursor Bugbot for commit 15af3d3. Configure here.}

[cursor]

Upsert method is identical to create, missing upsert behavior

High Severity

The upsert method is documented to "create or update a contact by email" if one already exists, but its implementation just delegates to this.create(options), which POSTs to /contacts — the exact same behavior as create. Since the codebase has a separate update method that PUTs to /contacts/{id}, the POST endpoint likely doesn't perform upsert logic. Users relying on upsert in signup flows would likely get duplicate-key errors for existing contacts instead of the documented update behavior.

 

^{Reviewed by Cursor Bugbot for commit 15af3d3. Configure here.}