feat(furniture): nightstand legs, bookcase columns/drawers, AC unit LG style, soundbars, wood-cube sconce

- NIGHTSTAND: optional legs with adjustable height (capped at 60% of total height)
- BOOKCASE: shelfColumns with vertical dividers, per-cell drawer fronts with handles,
  z-fighting fix between dividers and back panel, stale drawerCells pruned on grid shrink
- AC_UNIT: new 'lg' style with dark vent, grille lines, deflector flap, LG accent
- SPEAKER: new 'soundbar' variant (90/110/140cm) with grille, driver cones, LED strip;
  SpeakerMesh split into dispatcher + SpeakerCabinetMesh to keep hook order stable
- Wall light: new 'wood-cube' style (wooden block sconce with top/bottom glow)
- PropertiesPanel: tf() helper replaces repeated i18n.exists fallbacks; inline checkbox
  styles consolidated into styles.checkboxLabel
- Translations: en/ru entries for new property keys

apps/client/public/locales/en/translation.json

@@ -237,6 +237,13 @@
   "properties.windowSlopeDepth": "Reveal depth",
   "properties.openingFrameThickness": "Frame thickness",
   "properties.shelfRows": "Shelf rows",
+  "properties.shelfColumns": "Shelf columns",
+  "properties.drawerCells": "Drawers",
+  "properties.legs": "Legs",
+  "properties.legHeight": "Leg height",
+  "properties.acUnitStyleLabel": "Style",
+  "properties.acUnitStyle.generic": "Generic",
+  "properties.acUnitStyle.lg": "LG",
   "properties.hasBackPanel": "Back panel",
   "properties.curtainOpen": "Open",
   "properties.curtainLeftOpen": "Left open",

apps/client/public/locales/ru/translation.json

@@ -240,6 +240,13 @@
   "properties.windowSlopeDepth": "Глубина откоса",
   "properties.openingFrameThickness": "Толщина рамы",
   "properties.shelfRows": "Количество полок",
+  "properties.shelfColumns": "Количество колонок",
+  "properties.drawerCells": "Ящики",
+  "properties.legs": "Ножки",
+  "properties.legHeight": "Высота ножек",
+  "properties.acUnitStyleLabel": "Стиль",
+  "properties.acUnitStyle.generic": "Обычный",
+  "properties.acUnitStyle.lg": "LG",
   "properties.hasBackPanel": "Задняя стенка",
   "properties.curtainOpen": "Раскрытие",
   "properties.curtainLeftOpen": "Левая створка",