feat: make VM and live ISO match an installed Nomarchy

- Migrate VM and graphical ISO to home-manager.nixosModules.home-manager;
  drop the standalone-HM sudo-based activation script (ran HM against
  /root because HOME wasn't reset) in flake.nix, core/system/vm-guest.nix,
  hosts/live-iso.nix.
- Run swaybg as nomarchy-wallpaper.service instead of a silent Hyprland
  exec-once so failures surface in systemctl.
- Skip the battery monitor unit on hosts without /sys/class/power_supply/BAT*
  (VMs, desktops).
- Don't wrap walker --dmenu in uwsm-app; redirect setsid background std-fds
  in nomarchy-launch-walker so $(menu ...) in nomarchy-menu doesn't hang.
- Restart waybar/walker via systemctl --user rather than pkill + uwsm-app
  to stop the post-theme-switch color race.
- Wire nomarchy-restart-walker/-waybar into nomarchy-theme-set so themes
  that only change the imported CSS reload correctly.
- Waybar: pin #custom-nomarchy to the Nomarchy font and use the U+F000
  codepoint so the logo shows across all themes.
- Auto-install the correct icon-theme package per palette via a new
  nomarchyLib.iconThemePackage helper in lib/default.nix; Everforest now
  actually renders for summer-night.
- Pre-cache every theme's HM generation: new packages.allThemeVariants
  flake output and nomarchy-themes-prebuild script so theme switches are
  cache-only (no Stylix rebuild, no downloads).
- Add nomarchy-test-live-iso to boot the graphical ISO in QEMU the same
  way nomarchy-test-vm does, with virtio-gpu support added to live-iso.nix.
- Installer-generated home.nix/system.nix now ship a curated, commented
  app menu (btop/fastfetch/chromium on by default) plus optional system
  services (Docker, libvirtd, Tailscale, Syncthing, Flatpak, Steam).
- nomarchy-test-vm now wipes the stale nomarchy.qcow2 before launch.
- Remove obsolete GEMINI.md and PLAN.md.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

features/scripts/utils/nomarchy-launch-walker

@@ -3,14 +3,27 @@
 # Wrapper to launch walker with elephant provider, or fallback to rofi if walker is missing.
 
 if command -v walker >/dev/null 2>&1; then
-    # Ensure elephant is running before launching walker
+    # The setsid backgrounded commands below MUST redirect all std fds to
+    # /dev/null. If they inherit stdout from a $(...) caller (e.g. nomarchy-menu
+    # doing `$(menu ...)`), bash waits for those fds to close on every return,
+    # which hangs the terminal after each menu selection.
     if ! pgrep -x elephant > /dev/null; then
-        setsid uwsm-app -- elephant &
+        setsid uwsm-app -- elephant </dev/null >/dev/null 2>&1 &
+        disown
     fi
 
-    # Ensure walker service is running
     if ! pgrep -f "walker --gapplication-service" > /dev/null; then
-        setsid uwsm-app -- walker --gapplication-service &
+        setsid uwsm-app -- walker --gapplication-service </dev/null >/dev/null 2>&1 &
+        disown
+    fi
+
+    # dmenu mode reads stdin and is invoked many times in quick succession
+    # by nomarchy-menu. Wrapping each call in uwsm-app (systemd-run --scope)
+    # creates a fresh transient scope per invocation, which breaks chained
+    # submenus — subsequent walker calls don't see a usable stdin and exit
+    # without showing anything. Invoke walker directly for dmenu.
+    if [[ "$*" == *"--dmenu"* ]]; then
+        exec walker "$@"
     fi
 
     exec uwsm-app -- walker --width 644 --maxheight 300 --minheight 300 "$@"