Add guides/invite-users

[shehab-as]

Add how-to guide for Inviting users via API

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Note

Low Risk
Low risk documentation-only change that adds a new guide page and navigation entry with no runtime or API behavior impact.

Overview
Adds a new How-to Guide page, guides/invite-users.mdx, documenting how to list invites, create an invite (including permission/seat-limit notes), and revoke an invite via the API.

Updates docs.yml navigation to include the new Invite users guide under the Developer Guide section.

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