GHSA-w7cg-whh7-xp28: SiYuan: Stored XSS in Bazaar marketplace via package README event handlers

Summary renderPackageREADME in kernel/bazaar/readme.go renders a Bazaar package README from Markdown to HTML with the lute engine and SetSanitize(true). The lute sanitizer is an event-handler blocklist: allowAttr rejects only attribute names present in a fixed eventAttrs map copied from the w3schools legacy handler list. That map omits modern event handlers. onpointerover, onpointerdown, onauxclick, onbeforetoggle, onfocusin, onanimationstart, and ontransitionend are not in the list, so the sanitizer passes them through verbatim on any tag. The frontend assigns the rendered HTML to mdElement.innerHTML in app/src/config/bazaar.ts with no client-side DOMPurify on this path, into a normal element in the main document (no iframe, no sandbox). The kernel sends no Content-Security-Policy, X-Frame-Options, or X-Content-Type-Options header on any response, so an inline handler runs when its event fires. The README is rendered when an Administrator opens a package in Settings → Marketplace, after the one-time marketplace trust consent. Install is not required. Result: a third-party Bazaar package author runs JavaScript in the Administrator's authenticated SiYuan origin when the Administrator views and interacts with the package listing, and gains full control of the workspace. Affected siyuan-note/siyuan, <= 3.6.5 (latest release, 2026-04-21). Confirmed live-exploitable on the b3log/siyuan:v3.6.5 image; identical code on master HEAD. Condition: the Administrator has accepted the marketplace trust consent (bazaar.trust, default false) and browses community Bazaar packages. The lute dependency pin is github.com/88250/lute v1.7.7-0.20260419134724-bb68012f231d. Both the online browse path (getBazaarPackageREADME) and the installed-package path (getInstalledPlugin) reach the same sink. Root cause render/sanitizer.go:225-232 (lute): allowAttr(name) returns false only when name exists in the eventAttrs map, an attribute denylist rather than an allowlist. render/sanitizer.g