Built backup.html covering BACKUP-REG.md v2.4 in full: 7 backup groups, 20+ file-registry categories (~100 individual file paths), all 11 systems' LEGACY files, platform + per-system databases, snapshot retention, registry-of-registries. Added a live search box that filters+auto-expands matching categories, given the scale of this registry vs CLEAN-REG.md. Cross-linked into dir.html, nav.html, clean.html (all bumped to v1.2/v1.1) and system/index.html (v1.2). THIS TIME (per USR369 catching the gap on T572): also registered both clean.html AND backup.html in page-inventory.html (was missing entirely before, confirmed live). Checked site-index.html -- deliberately did NOT add entries there, since dir.html/nav.html aren't linked there either (it only links the raw STANDARDS-REG.md registry) -- adding clean/backup only would put them ahead of the older pages in discoverability. Left for T-PAGE-AUDIT to decide whether site-index.html should be restructured into real categories. All pages backed up before edit, JS syntax-checked before every deploy.