lint: admin-family gate-presence check for new /admin pages

Fast-follow from AYUD-112 (NOT a launch blocker). Pre-stage lint in .gitpush-pre.sh: any new src/app/**/page.tsx in an admin-gated family (/admin/*, /log) must contain isAdmin(user)+redirect gate else BLOCK (opt-out sentinel for intentional public pages). Mirrors venus VENUS-103. Closes inline-authz omission blind spot; until then solo content-trigger + self-tiering cover it.