fix: ensure system closure is installed for derivations needed by the installer

installer/auto-install.nix

@@ -53,14 +53,18 @@
       echo ">>> Running disko script..."
       ${diskoScript}
 
+      echo ">>> Copying system closure to target..."
+      # Copy the entire system closure without substitution
+      nix-store --store /mnt --load-db < <(nix-store --dump-db)
+      nix-copy-closure --to /mnt ${targetSystem} 2>/dev/null || true
+
       echo ">>> Running nixos-install..."
-      # Use only local store - don't fetch from binary cache or build
+      # Install with pre-built closure already in store
       nixos-install \
         --no-root-passwd \
         --root /mnt \
         --system ${targetSystem} \
-        --option substitute false \
-        --option build-use-sandbox false
+        --option substitute false
 
       echo ">>> Done. Rebooting."
       systemctl reboot