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/overlays/ScaleBar.tsx

@@ -0,0 +1,60 @@
+import styles from './scale-bar.module.css';
+
+interface ScaleBarProps {
+  readonly zoom: number;
+}
+
+/** Fixed pixel width of the scale bar on screen. */
+const BAR_WIDTH_PX = 100;
+
+/**
+ * Compute a "nice" real-world distance for the scale bar
+ * and the corresponding pixel width to display.
+ */
+function computeScaleInfo(zoom: number): { label: string; barPx: number } {
+  // zoom = pixels per meter
+  // BAR_WIDTH_PX pixels = BAR_WIDTH_PX / zoom meters
+  const rawMeters = BAR_WIDTH_PX / zoom;
+
+  // Find the nearest "nice" value
+  const niceValues = [
+    0.01, 0.02, 0.05, 0.1, 0.2, 0.25, 0.5,
+    1, 2, 5, 10, 20, 50, 100,
+  ];
+
+  let bestValue = niceValues[0];
+  let bestDiff = Math.abs(rawMeters - bestValue);
+  for (const v of niceValues) {
+    const diff = Math.abs(rawMeters - v);
+    if (diff < bestDiff) {
+      bestDiff = diff;
+      bestValue = v;
+    }
+  }
+
+  const barPx = bestValue * zoom;
+
+  let label: string;
+  if (bestValue >= 1) {
+    label = `${bestValue}m`;
+  } else {
+    label = `${Math.round(bestValue * 100)}cm`;
+  }
+
+  return { label, barPx };
+}
+
+export function ScaleBar({ zoom }: ScaleBarProps) {
+  const { label, barPx } = computeScaleInfo(zoom);
+
+  return (
+    <div className={styles.container}>
+      <div className={styles.bar} style={{ width: `${Math.round(barPx)}px` }}>
+        <div className={styles.tickLeft} />
+        <div className={styles.line} />
+        <div className={styles.tickRight} />
+      </div>
+      <span className={styles.label}>{label}</span>
+    </div>
+  );
+}