USR369 direction 08/25/26: build a maintenance schedule page with adjustable cadence, confirm/build an SOP-browsable HTML and a Tools HTML, and designate an owner for maintenance duties so new ones fold in without ad-hoc decisions each time. Built: (1) backend/api/critical/maintenance-schedule-api.php + maintenance-schedule-data.json -- get/update_duty/add_duty/set_owner actions, partial-update convention. (2) backend/standards/system/maintenance.html -- browsable, editable duty list (cadence dropdown + interval_days input, saves live via the API), owner strip, MAINTENANCE-LOG.md tail preview. (3) backend/standards/system/sop.html -- browsable, searchable, live-fetched SOP-INDEX.md viewer (same page family as dir.html/nav.html/clean.html/backup.html). Confirmed Tools HTML already existed (backend/tools/index.html, status DONE, updated same day) -- did not duplicate it. Designated Master[10] as the standing maintenance coordinator in the new data file and in SOP-HOUSEKEEPING-SCHEDULE.md (bumped v1.3->v1.4): new duty added (Master/Task List verify + close-out, weekly default, Master[10]-owned) plus two new sections (2B method, 2C control-panel description). page-inventory.html updated with both new pages.