Etherpad has stored XSS in HTML export via unescaped attribute-pool values

Fix: PR #7905 (ether/etherpad).

getHTMLFromAtext in src/node/utils/ExportHtml.ts interpolates values from the exportHtmlAdditionalTagsWithData plugin hook into span data-="" without HTML-attribute escaping. The value comes verbatim from the pad attribute pool, which a pad editor controls via a crafted changeset (only author attributes are validated; moveOpsToNewPool -> AttributePool.putAttrib stores any value). With a bundled plugin that registers the hook (ep_font_color / ep_font_size), an attribute value such as " onload="alert(1) is exported as `` and served as text/html, yielding stored XSS for any collaborator who opens the export.

Fix: escape the name and value via Security.escapeHTMLAttribute. PR #7905 also adds a startup warning when default/placeholder account or SSO credentials are configured (defense-in-depth, non-breaking).