feat: keymap/locale + form factor in installer; nm-applet visible by default

- Installer prompts for keyboard layout (with optional variant) and locale
  via curated short list + Other… fallback into the full localectl list;
  applies to the live session immediately (loadkeys + hyprctl) so the
  rest of the install types correctly. Generated system.nix emits
  console.keyMap, i18n.defaultLocale, and services.xserver.xkb.{layout,
  variant}.
- New nomarchy.{system,}.formFactor enum (laptop|desktop, default laptop).
  Installer auto-detects via /sys/class/power_supply/BAT* and lets the
  user flip the answer. Waybar drops the battery widget on desktop;
  battery-monitor service is gated on the same option.
- Lift waybar tray out of the collapsed group/tray-expander in the default
  theme so nm-applet's icon is visible without expanding the drawer.
- Live ISOs (TTY + graphical) get baseline mkDefault keyMap/locale so the
  installer's runtime override always wins.

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

features/desktop/waybar/config/config.jsonc

@@ -7,7 +7,7 @@
   "modules-left": ["custom/nomarchy", "hyprland/workspaces"],
   "modules-center": ["clock", "custom/update", "custom/voxtype", "custom/screenrecording-indicator", "custom/idle-indicator", "custom/notification-silencing-indicator"],
   "modules-right": [
-    "group/tray-expander",
+    "tray",
     "bluetooth",
     "network",
     "pulseaudio",
@@ -120,22 +120,6 @@
       "default": ["", "", ""]
     }
   },
-  "group/tray-expander": {
-    "orientation": "inherit",
-    "drawer": {
-      "transition-duration": 600,
-      "children-class": "tray-group-item"
-    },
-    "modules": ["custom/expand-icon", "tray"]
-  },
-  "custom/expand-icon": {
-    "format": "",
-    "tooltip": false,
-    "on-scroll-up": "",
-    "on-scroll-down": "",
-    "on-scroll-left": "",
-    "on-scroll-right": ""
-  },
   "custom/screenrecording-indicator": {
     "on-click": "nomarchy-cmd-screenrecord",
     "exec": "~/.config/nomarchy/default/waybar/indicators/screen-recording.sh",