Split shared host config into dedicated modules

- Add shared modules for boot, hardware, networking, input, and host defaults
- Move host-specific TOML flags to new option namespaces
- Update SSH and service defaults for the new layout

modules/nixos/shared/hardware/graphics/vaapi.nix

@@ -0,0 +1,29 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}: let
+  inherit (lib) mkIf mkOption types;
+  cfg = config.unexplrd.hardware.graphics.vaapi;
+in {
+  options.unexplrd.hardware.graphics.vaapi = mkOption {
+    type = types.nullOr (types.enum ["intel-media-driver" "nvidia"]);
+    default = null;
+  };
+
+  config = lib.mkMerge [
+    (mkIf (cfg == "intel-media-driver") {
+      hardware.graphics.extraPackages = with pkgs; [
+        intel-compute-runtime
+        intel-media-driver
+        vpl-gpu-rt
+      ];
+    })
+    (mkIf (cfg == "nvidia") {
+      hardware.graphics.extraPackages = with pkgs; [
+        nvidia-vaapi-driver
+      ];
+    })
+  ];
+}