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.

plasma-plugin/dev.emil.video/metadata.json

@@ -0,0 +1,17 @@
+{
+    "KPackageStructure": "Plasma/Wallpaper",
+    "KPlugin": {
+        "Authors": [
+            {
+                "Name": "Emil"
+            }
+        ],
+        "Id": "dev.emil.video",
+        "License": "GPL-3.0-or-later",
+        "Name": "Video Wallpaper",
+        "Version": "0.1.0",
+        "Description": "Plays a video file as the wallpaper, scaled to fill the screen"
+    },
+    "X-KDE-ParentApp": "org.kde.plasmashell",
+    "X-Plasma-API-Minimum-Version": "6.0"
+}