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>

themes/engine/scripts/nomarchy-theme-set

@@ -51,4 +51,15 @@ nomarchy-env-update
 
 nomarchy-theme-set-templates
 
+# Walker reads its CSS via @import of ~/.config/nomarchy/current/theme/apps/walker/style.css,
+# and waybar's shared fallback style does the same with waybar.css. HM's sd-switch
+# only restarts services whose unit *definition* changed, so when only the imported
+# file's contents change, neither gets reloaded. Restart them explicitly.
+command -v nomarchy-restart-walker >/dev/null 2>&1 && nomarchy-restart-walker || true
+command -v nomarchy-restart-waybar >/dev/null 2>&1 && nomarchy-restart-waybar || true
+
+# Reload the wallpaper — its ExecStart path is stable (~/.config/nomarchy/current/background)
+# so sd-switch does not detect a unit change when only the symlink target moves.
+systemctl --user restart nomarchy-wallpaper.service 2>/dev/null || true
+
 nomarchy-hook theme-set "$THEME_NAME"