SiYuan: authFilePublishAccess distinguishes hidden and forbidden documents from public and nonexistent ones, and issues a publish-auth cookie for documents it reports as forbidden

Summary /api/filetree/authFilePublishAccess is registered with CheckAuth only and is reachable anonymously. It never sets a failure code, so its outcome is signalled entirely by the response message and by whether a Set-Cookie header is present. Those two signals differ across access tiers, which...