update on docs and add 403 error page

[duharry0915]

Summary by cubic

Adds a new knowledge base page for API 403 errors and updates the docs navigation. Cleans up the drafts API schema by removing unused thread references.

• New Features

  • Added "API 403 error" KB page with common causes and fixes.
  • Linked the page in docs under Troubleshooting with a ban icon.

• Refactors

  • Removed threads import from fern/definition/drafts.yml.
  • Removed thread_id from Draft and DraftItem types.

^{Written for commit 2a58fe3. Summary will update on new commits.}

[github-actions]

✨ API Changes

# API Changelog n/a vs. n/a

## GET /v0/drafts
- :warning: removed the required property 'drafts/items/thread_id' from the response with the '200' status


## GET /v0/drafts/{draft_id}
- :warning: removed the required property 'thread_id' from the response with the '200' status


## GET /v0/inboxes/{inbox_id}/drafts
- :warning: removed the required property 'drafts/items/thread_id' from the response with the '200' status


## POST /v0/inboxes/{inbox_id}/drafts
- :warning: removed the required property 'thread_id' from the response with the '200' status


## GET /v0/inboxes/{inbox_id}/drafts/{draft_id}
- :warning: removed the required property 'thread_id' from the response with the '200' status


## PATCH /v0/inboxes/{inbox_id}/drafts/{draft_id}
- :warning: removed the required property 'thread_id' from the response with the '200' status


## GET /v0/pods/{pod_id}/drafts
- :warning: removed the required property 'drafts/items/thread_id' from the response with the '200' status


## GET /v0/pods/{pod_id}/drafts/{draft_id}
- :warning: removed the required property 'thread_id' from the response with the '200' status

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

[github-actions]

🌿 Preview your docs: https://agentmail-preview-de18ccbf-851a-4991-a286-a360d66a91a5.docs.buildwithfern.com

[cubic-dev-ai]

No issues found across 3 files