feat: complete house plan maker application

Full-featured house/apartment floor plan editor with:

- Turborepo monorepo (React/Vite client, Fastify/Prisma server, shared Zod schemas)
- 2D room editor with walls, doors, windows, furniture, electrical elements
- 3D room preview with Three.js (auto-hide nearest walls, bird's eye default)
- Wall projection views with interactive drag (elevation, position)
- Apartment floor plan view with room positioning
- Copy/paste, alignment tools, measurement tool, annotations
- Item-attached annotations with leader lines (visible on projections)
- Door open direction (LEFT/RIGHT/INWARD/OUTWARD) with swing arc
- Floor type textures (wood, tile, concrete, laminate, herringbone)
- Wall color picker for 3D view
- Furniture: bed, desk, wardrobe, sofa, table, chair, shelf, nightstand, dresser, bookcase, TV (with stand toggle), AC unit
- Furniture elevation support (wall-mounted items)
- Auto-save with dirty state tracking, batch save API
- Rotation-aware collision detection (SAT/OBB) with 3D elevation check
- Rotation-aware hit testing
- i18n (English/Russian) with locale-aware number formatting
- Dark mode with system preference detection
- Undo/redo, keyboard shortcuts, scale bar
- PDF/PNG/JSON export and JSON import
- Focus trap modal, toast notifications, tooltips
- Responsive layout with overlay palettes

apps/client/src/components/editor/tools/FurnitureTool.ts

@@ -0,0 +1,73 @@
+import type { Point, FurnitureItem } from '@house-plan-maker/shared';
+import { generateLocalId } from '../utils/geometry';
+import type { FurnitureDef } from '../symbols/furniture';
+
+export interface FurniturePlacementPreview {
+  readonly x: number;
+  readonly y: number;
+  readonly width: number;
+  readonly depth: number;
+  readonly rotation: number;
+  readonly isValid: boolean;
+}
+
+/**
+ * Compute furniture placement preview.
+ * The x,y represents the top-left corner of the furniture piece.
+ * The cursor world point is treated as the desired center, so we offset
+ * by half-width and half-depth to get the top-left corner.
+ */
+export function computeFurniturePreview(
+  worldPoint: Point,
+  furnitureDef: FurnitureDef,
+  rotation: number = 0,
+): FurniturePlacementPreview {
+  return {
+    x: worldPoint.x - furnitureDef.width / 2,
+    y: worldPoint.y - furnitureDef.depth / 2,
+    width: furnitureDef.width,
+    depth: furnitureDef.depth,
+    rotation,
+    isValid: true,
+  };
+}
+
+/**
+ * Create a FurnitureItem from placement data.
+ */
+export function createFurnitureItemFromPlacement(
+  roomId: string,
+  preview: FurniturePlacementPreview,
+  furnitureDef: FurnitureDef,
+): FurnitureItem {
+  return {
+    id: generateLocalId(),
+    roomId,
+    type: furnitureDef.type,
+    x: preview.x,
+    y: preview.y,
+    width: preview.width,
+    depth: preview.depth,
+    height: furnitureDef.height,
+    rotation: preview.rotation,
+    elevationFromFloor: furnitureDef.type === 'AC_UNIT' ? 2.2 : furnitureDef.height <= 0.05 ? 1.2 : 0,
+    label: furnitureDef.label,
+  };
+}
+
+/** Rotate a furniture item by the given delta in degrees. */
+export function rotateFurniture(item: FurnitureItem, deltaDeg: number): FurnitureItem {
+  return {
+    ...item,
+    rotation: (item.rotation + deltaDeg) % 360,
+  };
+}
+
+/** Move a furniture item to a new position. */
+export function moveFurniture(item: FurnitureItem, newPos: Point): FurnitureItem {
+  return {
+    ...item,
+    x: newPos.x,
+    y: newPos.y,
+  };
+}