fix: complete hybridGPU wiring + make state-derived options overridable

Two related fixes that together close the "minimal wiring" gap behind
`nomarchy.system.features.hybridGPU`.

1. Complete the NVIDIA driver stack inside hardware.nix's hybridGPU
   mkIf block.

   Before: `hybridGPU = true` enabled supergfxd and... that was it.
   supergfxd manages mode switching by black/unblacklisting the nvidia
   kernel module, but without the rest of the NVIDIA stack actually
   loaded the dGPU has no driver to drive. Hyprland/Wayland silently
   stayed on the iGPU regardless of mode.

   After: hybridGPU=true also wires
     services.xserver.videoDrivers = ["nvidia"]   (loads the driver
                                                   under Wayland too)
     hardware.graphics.{enable,enable32Bit}
     hardware.nvidia.modesetting.enable           (required for
                                                   Wayland)
     hardware.nvidia.powerManagement.enable
     hardware.nvidia.package = config.boot.kernelPackages
                                      .nvidiaPackages.stable
     boot.kernelParams += "nvidia-drm.modeset=1"

   All wired with lib.mkDefault so a downstream system.nix can pin a
   beta driver, flip to the open kernel module, or set
   `hardware.nvidia.prime.{offload.enable, intelBusId, nvidiaBusId}`
   for render-offload. The bus IDs are per-machine (find via
   `lspci -D`) so they stay user-supplied; docs/OPTIONS.md has the
   full recipe.

2. Add lib.mkDefault to every state.json-derived assignment in
   core/system/state.nix and core/home/state.nix.

   Same priority bug on both sides: assignments like
   `features.hybridGPU = systemState.features.hybridGPU or false`
   landed at default priority. A downstream system.nix saying
   `nomarchy.system.features.hybridGPU = true` would then conflict
   with the state-derived value at the same priority, and Nix would
   refuse the merge with "conflicting definition values" — the
   user's override couldn't take effect.

   Verified by an explicit eval: extending the default nixosConfig
   with `nomarchy.system.features.hybridGPU = true` now resolves
   cleanly and the full driver stack engages.

   Side-effect: core/system/state.nix now reads from
   lib/state-schema.nix like the home side does, completing the
   schema-centralization started two batches ago.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

core/system/hardware.nix

@@ -70,8 +70,47 @@ in
     })
 
     (mkIf config.nomarchy.system.features.hybridGPU {
+      # supergfxd manages mode switching (Integrated / Hybrid / Vfio /
+      # AsusEgpu). It blacklists/unblacklists the nvidia kernel module via
+      # /etc/modprobe.d/ depending on the active mode. ExecStartPre sleep
+      # gives udev time to settle so the daemon doesn't see a half-attached
+      # GPU on cold boot.
       services.supergfxd.enable = true;
       systemd.services.supergfxd.serviceConfig.ExecStartPre = "-${pkgs.coreutils}/bin/sleep 5";
+
+      # Load the NVIDIA driver so the dGPU has something to drive. Without
+      # these, supergfxd switches modes successfully but the X/Wayland
+      # stack has no NVIDIA driver loaded — render-offload silently no-ops
+      # and Hyprland renders everything on the iGPU regardless of mode.
+      # mkDefault throughout so downstream system.nix can override
+      # (pin to a beta driver, flip to the open kernel module, etc.).
+      services.xserver.videoDrivers = lib.mkDefault [ "nvidia" ];
+      hardware.graphics.enable = lib.mkDefault true;
+      hardware.graphics.enable32Bit = lib.mkDefault true;
+      hardware.nvidia = {
+        modesetting.enable = lib.mkDefault true;
+        powerManagement.enable = lib.mkDefault true;
+        open = lib.mkDefault false;
+        package = lib.mkDefault config.boot.kernelPackages.nvidiaPackages.stable;
+      };
+      # Required for Wayland compositors (Hyprland) to render via NVIDIA.
+      boot.kernelParams = [ "nvidia-drm.modeset=1" ];
+
+      # PRIME render-offload (the part that lets `nvidia-offload <cmd>`
+      # actually use the dGPU) needs bus IDs, which are per-machine.
+      # We deliberately don't enable `hardware.nvidia.prime.offload.enable`
+      # here — without the correct intelBusId / nvidiaBusId the nvidia
+      # kernel module panics on load. The user adds this to their own
+      # /etc/nixos/system.nix after running `lspci -D`:
+      #
+      #   hardware.nvidia.prime = {
+      #     offload.enable = true;
+      #     offload.enableOffloadCmd = true;
+      #     intelBusId  = "PCI:0:2:0";   # or amdgpuBusId for AMD iGPU
+      #     nvidiaBusId = "PCI:1:0:0";
+      #   };
+      #
+      # See docs/OPTIONS.md for the full recipe.
     })
   ];
 }