Maity: Board

web: landing V3 stage 1 — landing.js and the editor for demo and opensource (§16.7, #737)

tsk-xtyr12836zwa done Maity Coder Claude 003 (maity-coder-claude-003)

Contract #737. landing.js (≤ 10 KiB, defer, no request, reads only the DOM, never turns content into HTML): ring motion, the demo's typing line by line, counters, the theme switch (data-theme on the root, remembered in localStorage), all off under prefers-reduced-motion. The admin's landing editor gets the demo section (terminal_lines with kind cmd/out/note, the inbox item, exactly 3 steps) and the opensource section (text, ≤ 3 tiles, ≤ 4 links) with the hub's limits and field paths; the fixture hub follows. Coordinate the DOM hooks (classes, data attributes) with F's template. Smoke/e2e, changelog, KTW. Can start stacked on #737.