feat(install): add disko direct-url workflow

docs/install-help.txt

@@ -1,22 +1,37 @@
 Nanuqsaurus NixOS installer
 ===========================
 
-Run the non-interactive installer:
+Direct-from-URL install (wipes the whole disk)
+---------------------------------------------
+
+Pick a stable disk path (prefer /dev/disk/by-id/*) and run:
+
+  sudo nix --experimental-features "nix-command flakes" \
+    run github:nix-community/disko/latest#disko-install -- \
+    --mode format \
+    --flake "git+https://codeberg.org/<owner>/<repo>.git#nanuqsaurus" \
+    --disk main /dev/disk/by-id/<your-disk> \
+    --mount-point /mnt
+
+
+ISO shortcut
+------------
+
+If you are using the custom ISO from this repo, it embeds the flake at /etc/nixos.
+You can run the wrapper script (defaults: DISK=/dev/vda, TARGET_HOST=nanuqsaurus):
 
   sudo /etc/nixos/scripts/install-btrfs.sh
 
 
-Optionally set DISK and TARGET_HOST (defaults: DISK=/dev/vda, TARGET_HOST=nanuqsaurus)
+Optionally set DISK, TARGET_HOST, and FLAKE:
 
-  sudo DISK=/dev/vda TARGET_HOST=nanuqsaurus /etc/nixos/scripts/install-btrfs.sh
+  sudo DISK=/dev/disk/by-id/<your-disk> TARGET_HOST=nanuqsaurus \
+    FLAKE="github:<owner>/<repo>" \
+    /etc/nixos/scripts/install-btrfs.sh
 
 
-The script wipes the whole disk, creates Btrfs subvolumes (root, home, nix), copies the flake, generates hardware config, and installs. It writes host files under `/etc/nixos/hosts/local-<hostname>.nix` and `local-<hostname>-hardware.nix` (kept local to the machine).
-
-
-If you need a more custom setup please run the partitioning manually, mount the target to /mnt and then install the system:
-
-  nixos-install --root /mnt --flake "/mnt/etc/nixos#local-${TARGET_HOST}" --no-root-passwd
+This uses disko to create a GPT disk with a 550M EFI partition and a Btrfs partition
+containing subvolumes root, home, and nix, mounted with compress=zstd.
 
 
 After install finishes, reboot into the new system.