Use legacy 580.xx NVIDIA driver for Quadro M2000 (Maxwell)

The latest 595.x driver dropped Maxwell GPU support. The Quadro M2000
(GM206) requires the legacy_580 branch for CUDA/NVENC to function.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

hosts/hardware/FredOS-Mediaserver.nix

@@ -65,6 +65,7 @@
     modesetting.enable = true;
     open = false; # Maxwell architecture does not support the open kernel module
     nvidiaSettings = false; # headless server, no settings GUI needed
+    package = config.boot.kernelPackages.nvidiaPackages.legacy_580;
   };
   services.xserver.videoDrivers = [ "nvidia" ];