Jellyfin: hardware video decoding (jellyfin.hardwareDecoding)

Jellyfin Desktop hard-sets mpv's hwdec=auto-copy, whose probe list leaves
out V4L2 M2M, and the Flatpak can't see the Frame's V4L2 decoder. An
LD_PRELOAD shim (preloaded straight from the store, only that path exposed
read-only) rewrites hwdec to v4l2m2m-copy,auto-copy; devices=all makes the
decoder visible. Overrides via nix-flatpak, or a home-manager-owned override
file without it.

template/home.nix

@@ -54,5 +54,8 @@
   #     frameControls.enable = true;
   #   };
   #   firefox.enable = true;             # launcher for the Firefox Flatpak
+  #   # Hardware video decoding in the Jellyfin Desktop Flatpak (install
+  #   # org.jellyfin.JellyfinDesktop yourself); gives it devices=all:
+  #   jellyfin.hardwareDecoding.enable = true;
   # };
 }