Add Steam Deck (nix-deck) configuration with Jovian-NixOS and remote building

- Add Jovian-NixOS integration for Steam Deck hardware support
- Create nix-deck machine configuration with SteamOS role
- Add jovian-compat.nix for NixOS 25.05 compatibility (remove in 25.11+)
- Create remote-build role for distributed builds
- Configure zix790prors as build host
- Configure nix-book and nix-deck to use remote builder with fallback
- Add comprehensive setup documentation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

roles/remote-build/default.nix

@@ -0,0 +1,127 @@
+{ lib, config, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.roles.remote-build;
+in
+{
+  options.roles.remote-build = {
+    enableBuilder = mkOption {
+      type = types.bool;
+      default = false;
+      description = "Enable this machine as a remote build host for other machines";
+    };
+
+    builderUser = mkOption {
+      type = types.str;
+      default = "nix-builder";
+      description = "User account for remote builders to connect as";
+    };
+
+    builders = mkOption {
+      type = types.listOf (types.submodule {
+        options = {
+          hostName = mkOption {
+            type = types.str;
+            description = "Hostname or IP address of the build machine";
+          };
+
+          systems = mkOption {
+            type = types.listOf types.str;
+            default = [ "x86_64-linux" ];
+            description = "Supported systems";
+          };
+
+          maxJobs = mkOption {
+            type = types.int;
+            default = 8;
+            description = "Maximum number of parallel build jobs";
+          };
+
+          speedFactor = mkOption {
+            type = types.int;
+            default = 2;
+            description = "Speed factor compared to local building (higher = prefer remote)";
+          };
+
+          supportedFeatures = mkOption {
+            type = types.listOf types.str;
+            default = [ "nixos-test" "benchmark" "big-parallel" "kvm" ];
+            description = "Supported build features";
+          };
+
+          sshUser = mkOption {
+            type = types.str;
+            default = "nix-builder";
+            description = "SSH user for connecting to the builder";
+          };
+
+          sshKey = mkOption {
+            type = types.nullOr types.path;
+            default = null;
+            description = "Path to SSH private key for authentication";
+          };
+        };
+      });
+      default = [];
+      description = "List of remote build machines to use";
+    };
+
+    fallbackToLocalBuild = mkOption {
+      type = types.bool;
+      default = true;
+      description = "Fallback to local building if remote builders are unavailable";
+    };
+  };
+
+  config = mkMerge [
+    # Builder host configuration
+    (mkIf cfg.enableBuilder {
+      # Create dedicated builder user
+      users.users.${cfg.builderUser} = {
+        isSystemUser = true;
+        group = cfg.builderUser;
+        description = "Nix remote build user";
+        home = "/var/lib/${cfg.builderUser}";
+        createHome = true;
+        shell = pkgs.bashInteractive;
+        openssh.authorizedKeys.keyFiles = [];  # Will be populated by client machines
+      };
+
+      users.groups.${cfg.builderUser} = {};
+
+      # Allow builder user to perform builds
+      nix.settings.trusted-users = [ cfg.builderUser ];
+
+      # Allow remote builds
+      services.openssh.enable = true;
+
+      # Ensure nix-daemon is accessible
+      nix.settings.allowed-users = [ "*" ];
+    })
+
+    # Client configuration (machines using remote builders)
+    (mkIf (cfg.builders != []) {
+      nix.buildMachines = map (builder: {
+        hostName = builder.hostName;
+        systems = builder.systems;
+        maxJobs = builder.maxJobs;
+        speedFactor = builder.speedFactor;
+        supportedFeatures = builder.supportedFeatures;
+        sshUser = builder.sshUser;
+        sshKey = builder.sshKey;
+      }) cfg.builders;
+
+      nix.distributedBuilds = true;
+
+      # Use substitutes from remote builders
+      nix.extraOptions = ''
+        builders-use-substitutes = true
+      '';
+
+      # Fallback to local build if remote unavailable
+      nix.settings.fallback = cfg.fallbackToLocalBuild;
+    })
+  ];
+}