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.

packages/shared/src/types/elements.ts

@@ -221,6 +221,7 @@ export const ELECTRICAL_TYPES = [
   'LIGHT_CEILING',
   'LIGHT_WALL',
   'CABLE_ROUTE',
+  'WALL_CABLE',
 ] as const;
 export type ElectricalType = (typeof ELECTRICAL_TYPES)[number];