Add troubleshooting for write access error in web editor

[mintlify]

Summary

• Added troubleshooting section to the web editor publish page for the "You don't have write access to this repo" error
• Included screenshot showing the error message
• Documented two solutions: getting repo write access or unauthorizing GitHub account

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Note

Low Risk
Documentation-only changes (new page + nav entry) with no runtime, security, or data-handling impact.

Overview
Adds a new editor/troubleshooting doc page for the web editor that explains the "You don't have write access to this repo" publish error, including a screenshot and two recommended fixes (grant repo write access or unauthorize GitHub so the Mintlify app signs commits).

Updates docs.json navigation to surface the new Troubleshooting page under the Web editor section.

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