docs(inboxes): Authorize Inbox returns api_key_id and instructions

[sidharth0612]

Summary

Pairs with agentmail-to/agentmail-api#1332, which thins the POST /v0/inboxes/{inbox_id}/authorize response to { api_key_id, instructions }.

• Fern definition: the endpoint now returns AuthorizeInboxResponse instead of api-keys.PublicKeyCredential. instructions is typed as the literal "Authorization complete. Return to browser." so SDK regenerations keep the sentence fixed.
• AgentID Sign-In guide: the authorize examples print api_key_id and instructions, and the prose points readers to Get API Key under Check activation for status.
• Changelog: a 2026-09-16 entry with the migration (read status from GET /v0/api-keys/{api_key_id}).

Test plan

• fern check passes, 0 errors, warning count unchanged from main

🤖 Generated with Claude Code

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✨ API Changes

# API Changelog n/a vs. n/a


## API Changes

### POST /v0/inboxes/{inbox_id}/authorize
- :warning: removed the required property `created_at` from the response with the `202` status
- :warning: removed the required property `created_by` from the response with the `202` status
- :warning: removed the required property `name` from the response with the `202` status
- :warning: removed the required property `permissions` from the response with the `202` status
- :warning: removed the required property `type` from the response with the `202` status
- :warning: removed the required property `updated_at` from the response with the `202` status
-  removed the optional property `client_id` from the response with the `202` status
-  removed the optional property `expires_at` from the response with the `202` status
-  removed the optional property `inbox_id` from the response with the `202` status
-  removed the optional property `pod_id` from the response with the `202` status
-  removed the optional property `public_key` from the response with the `202` status
-  removed the optional property `status` from the response with the `202` status
-  removed the optional property `used_at` from the response with the `202` status
-  added the required property `instructions` to the response with the `202` status

💡 Download api-changelog-diff artifact or tag @fern Writer in #github-prs for changelog.

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