Landing B7: one two-column grid, hairline rows, FR+EN, dark

[rmzlb]

Landing rebuilt on the B7 structure, FR + EN, light + dark.

• One two-column grid everywhere: sticky title on the left, hairline rows on the right. Header unchanged.
• Footer in columns with the dot field and floating tanuki (shared with /compare, checked).
• Board tabs really filter, R replays the MAR-12 flow, status pills are mono text with a square.
• Film and demo start on their poster and only load the video on click (no autoplay, no 2 videos on page open).
• Header, content and footer share the same right edge (1356 px).

Checks: npm run build passes; no tsc error in touched files (5 pre-existing elsewhere). Pre-existing on main, not touched here: 3 positioning.test.ts failures (222 vs 231 endpoints) and npm run lint has no eslint.config.js.