feat(installer): add one-file installer build and custom install ISO

Replace old_installer.py with a curses TUI installer packaged as a
one-file PyInstaller binary (python/installer/build.py, wrapped by
python/installer/package.nix). The default .#installer is patched to run
on foreign Linux live media; the new .#installer-nixos variant keeps its
Nix store interpreter so it runs on NixOS.

Add systems/iso, a minimal NixOS install CD with kernel 6.18 and ZFS 2.4
matching the deployed systems and the installer on PATH; build it with
nix build .#iso. Shared logging and subprocess helpers move out of
common.py into python/logging_config.py and python/process.py.

python/installer/tui.py

@@ -5,32 +5,12 @@ from __future__ import annotations
 import curses
 import logging
 from collections import defaultdict
-from subprocess import PIPE, Popen
+
+from python.process import run_output
 
 logger = logging.getLogger(__name__)
 
 
-def bash_wrapper(command: str) -> str:
-    """Execute a bash command and capture the output.
-
-    Args:
-        command (str): The bash command to be executed.
-
-    Returns:
-        Tuple[str, int]: A tuple containing the output of the command (stdout) as a string,
-        the error output (stderr) as a string (optional), and the return code as an integer.
-    """
-    logger.debug(f"running {command=}")
-    # This is a acceptable risk
-    process = Popen(command.split(), stdout=PIPE, stderr=PIPE)
-    output, _ = process.communicate()
-    if process.returncode != 0:
-        error = f"Failed to run command {command=} return code {process.returncode=}"
-        raise RuntimeError(error)
-
-    return output.decode()
-
-
 class Cursor:
     """Cursor class."""
 
@@ -144,7 +124,7 @@ def get_device(raw_device: str) -> dict[str, str]:
 def get_devices() -> list[dict[str, str]]:
     """Get a list of devices."""
     # --bytes
-    raw_devices = bash_wrapper("lsblk --paths --pairs").splitlines()
+    raw_devices = run_output(("lsblk", "--paths", "--pairs")).splitlines()
     return [get_device(raw_device) for raw_device in raw_devices]
 
 
@@ -305,12 +285,12 @@ def get_device_id_mapping() -> dict[str, set[str]]:
     Returns:
         list[str]: the list of device ids
     """
-    device_ids = bash_wrapper("find /dev/disk/by-id -type l").splitlines()
+    device_ids = run_output(("find", "/dev/disk/by-id", "-type", "l")).splitlines()
 
     device_id_mapping: dict[str, set[str]] = defaultdict(set)
 
     for device_id in device_ids:
-        device = bash_wrapper(f"readlink -f {device_id}").strip()
+        device = run_output(("readlink", "-f", device_id)).strip()
         device_id_mapping[device].add(device_id)
 
     return device_id_mapping