Teaser: Phosphor cursor and icons, a desktop app scene, new render for the site

- The mouse cursor and the blocker-list icons are Phosphor files (media/teaser/icons, copied unchanged by
  tools/site-icons.ts) shown as CSS masks; no hand-written SVG left in media/teaser.
- The no-handmade-svg guard now covers media/teaser: no inline SVG, every referenced icon is a vendored Phosphor file,
  byte-equal to the package.
- New 6-bar desktop scene before the Submit card: real frames of apps/desktop in fixture mode (media/teaser/desktop.ts,
  captured headlessly) in a CSS window: portfolio across studios, the release track of both stores, the Growth chart
  with its tooltip, the Cmd+K palette, a price-sheet dry-run diff, the confirm dialog, and Submit for review left to
  the console. Music and timeline follow (26 bars, 48.75 s).
- End card: "Desktop app for macOS, Windows, Linux".
- site/img/teaser.mp4 (1280x720 H.264, about 3 MB) and its poster re-rendered; ?v= bumped, captions say 49 s.

media/teaser/icons/arrow-right-bold.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 256 256" fill="currentColor"><path d="M224.49,136.49l-72,72a12,12,0,0,1-17-17L187,140H40a12,12,0,0,1,0-24H187L135.51,64.48a12,12,0,0,1,17-17l72,72A12,12,0,0,1,224.49,136.49Z"/></svg>