Render the ice as long videos and play them as wallpapers

render_wallpaper.py drives headless Firefox frame by frame (four at a time,
resuming where it stopped), then ffmpeg. Thirty seconds at 30 fps is exactly
one plasma cycle, so frame 900 meets frame 0 and the loop has no seam.

plasma-plugin/dev.emil.video is a minimal Plasma 6 video wallpaper: one file
per screen, filling the screen, looping. H.264 is encoded Baseline because
Qt here decodes through openh264, which rejects High profile and leaves a
frozen frame; a new source also has to be played explicitly.

The #shot hash learned info=0 to hide the on-screen hint for renders.

build_plasma.py

@@ -79,6 +79,7 @@ const shot = location.hash.startsWith('#shot');
 const shotParams = new URLSearchParams(location.hash.slice(1));
 let mouseX = Number(shotParams.get('mx') ?? 0.5), mouseY = Number(shotParams.get('my') ?? 0.5);
 let speed = 1, time = Number(shotParams.get('t') ?? 0), previous;
+if (shotParams.get('info') === '0') document.getElementById('info').style.display = 'none';
 addEventListener('pointermove', e => { mouseX = e.clientX / innerWidth; mouseY = 1 - e.clientY / innerHeight; });
 addEventListener('keydown', e => {
   if (e.key === '-' || e.key === '_') speed = Math.max(0.125, speed / 2);