CVE-2026-74904: SiYuan: 17 block metadata/content endpoints in kernel/api/block.go have zero publish-access filtering, reachable by anonymous publish-mode readers

17 handlers in kernel/api/block.go, all gated only by model.CheckAuth with no admin-role requirement, return block content-derived text, structural metadata, or existence information for any block ID supplied, with no access check anywhere in the handler or, for the ones checked in detail, the model functions they call. This is CWE-862 (Missing Authorization), the same class as the companion advisories from this review round, found in a different file via a systematic bulk check rather than manual inspection of each function individually.