feat: nomarchy-install — guided live-ISO installer (disko + mkFlake)

Ported from the previous iteration's installer (3bdfc35), adapted to the
mkFlake world. gum TUI: disk pick, optional LUKS2, user/hostname/timezone,
DMI → nixos-hardware autodetection (hardware-db.sh). disko partitions
GPT + 1 GiB ESP + BTRFS subvolumes; the generated machine flake lands at
~user/.nomarchy (one mkFlake call, /etc/nixos symlinks to it) and
nixos-install makes it bootable (UEFI/systemd-boot, v1 single disk).

Offline by construction: the target flake.lock is composed from the rev
the ISO was built from (compose-lock.py), `nix flake archive` seeds the
target store, and the ISO pre-builds the template system + desktop.
First boot lands themed: the HM generation is pre-activated in chroot.

mkFlake grows two things for this: hardwareProfile now also takes a list
(autodetection emits several common-* modules), and installed systems get
the standalone home-manager CLI from the pinned input. Unattended mode
(NOMARCHY_UNATTENDED=1 + env) documented in docs/TESTING.md §4.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

hosts/live.nix

@@ -64,6 +64,7 @@
     The graphical session autologins as '${username}' (no password).
     Theme switching:  nomarchy-theme-sync apply <name>   (or SUPER+T)
     Wallpapers:       nomarchy-theme-sync bg next        (or SUPER+SHIFT+T)
+    Install to disk:  nomarchy-install
     The flake lives at ~/.nomarchy.
   '';
 
@@ -76,7 +77,7 @@
       # Welcome toast once the session is up (concatenated onto the
       # base exec-once list).
       exec-once = [
-        "sh -c 'sleep 3; notify-send -a Nomarchy \"Welcome to Nomarchy\" \"SUPER+Return terminal · SUPER+T themes · SUPER+SHIFT+T wallpaper\"'"
+        "sh -c 'sleep 3; notify-send -a Nomarchy \"Welcome to Nomarchy\" \"SUPER+Return terminal · SUPER+T themes · install with nomarchy-install\"'"
       ];
     };
   };