feat: add WALL_CABLE electrical type and room outlet/switch count stats

Add wall cable item — a bare cable exit from the wall for direct
consumer connection without an outlet. Includes 2D symbol (circle +
cable stub), 3D mesh (round plate + protruding cable), and palette entry.

Also add outlet and switch count metrics to the room info section in
the properties panel.

apps/client/src/components/editor/PropertiesPanel.tsx

@@ -151,6 +151,14 @@ export function PropertiesPanel() {
           )}
           <PropertyRow label={t('properties.wallHeight')} value={`${room.wallHeight}m`} />
           <PropertyRow label={t('properties.plinthHeight')} value={`${Math.round(room.plinthHeight * 1000) / 10}cm`} />
+          <PropertyRow
+            label={t('properties.outletCountStat')}
+            value={String(electricalItems.filter((e) => e.type === 'OUTLET').reduce((sum, e) => sum + Math.max(1, e.count), 0))}
+          />
+          <PropertyRow
+            label={t('properties.switchCountStat')}
+            value={String(electricalItems.filter((e) => e.type === 'SWITCH').length)}
+          />
           {/* Stretch ceiling drop (натяжной потолок). Stored in meters,
               edited in cm for ergonomics. 0 = disabled. */}
           <EditablePropertyRow