feat(install): #59 NVIDIA commented system.nix guidance

When hardwareProfile includes common-gpu-nvidia, emit a comment-only
plain NixOS block (PRIME / powerManagement / open-module) in the
installer region of system.nix — same pattern as ROCm/NPU opt-ins.
HARDWARE.md §6 product direction marked shipped. Close #59.

Verified: V0 (patch-template smoke + negative + bash -n).

pkgs/nomarchy-install/nomarchy-install.sh

@@ -411,6 +411,10 @@ if [[ ${#HW_NOMARCHY[@]} -gt 0 ]]; then
         esac
     done
 fi
+# NVIDIA is a nixos-hardware MODULE only (no nomarchy.hardware.nvidia.*) —
+# still emit commented plain-NixOS guidance in system.nix (BACKLOG #59).
+has_nvidia=false
+[[ " ${HW_PROFILES[*]:-} " == *" common-gpu-nvidia "* ]] && has_nvidia=true
 is_laptop=false
 [[ " ${HW_PROFILES[*]:-} " == *" common-pc-laptop "* ]] && is_laptop=true
 thermald=false
@@ -452,6 +456,7 @@ python3 "$SHARE/patch-template.py" "$FLAKE_DIR" <<PYJSON
     "amd": $has_amd,
     "fingerprint": $has_fp,
     "cameraIr": $has_camera_ir,
+    "nvidia": $has_nvidia,
     "npu": $(if [[ -n "$NPU_VENDOR" ]]; then printf '%s' "$NPU_VENDOR" | python3 -c 'import json,sys; print(json.dumps(sys.stdin.read().rstrip("\n")))'; else echo null; fi)
   },
   "resumeOffset": $resume_json,