fix: physical conveyor realism - belt at 0.7m, item rides ON belt

- Create physicalLayout.ts with all dimensions
- Update conveyorPath.ts to use correct belt height
- Rebuild ConveyorBelt with support legs, rollers, drive motor
- Item Y = BELT_TOP_Y + itemHeight/2

src/domain/physicalLayout.ts

@@ -0,0 +1,128 @@
+/**
+ * Physical Layout — единый источник правды для размеров 3D сцены.
+ * Все размеры в метрах (1 Three.js unit = 1 meter).
+ * 
+ * Reference: OZON Track 3 specification
+ * - Рабочая зона: 6000×10000 мм
+ * - Конвейер: ширина 500мм, высота 700мм
+ * - Скорость полотна: 1 м/с
+ */
+
+// =========================================================
+// Workspace
+// =========================================================
+export const WORKSPACE_WIDTH_M = 6.0;
+export const WORKSPACE_LENGTH_M = 10.0;
+
+// =========================================================
+// Conveyor dimensions (per OZON spec)
+// =========================================================
+export const CONVEYOR_WIDTH_M = 0.5;          // 500mm belt width
+export const CONVEYOR_HEIGHT_M = 0.7;          // 700mm belt top surface from floor
+export const CONVEYOR_SPEED_MPS = 1.0;         // 1 m/s belt speed
+export const CONVEYOR_LENGTH_M = 8.5;          // Total belt length
+
+// Belt structure
+export const BELT_THICKNESS_M = 0.015;         // 15mm belt thickness
+export const BELT_TOP_Y = CONVEYOR_HEIGHT_M;   // Top surface where items ride
+export const BELT_BOTTOM_Y = CONVEYOR_HEIGHT_M - BELT_THICKNESS_M;
+
+// Rollers (under/inside belt)
+export const ROLLER_RADIUS_M = 0.04;           // 40mm radius
+export const ROLLER_DIAMETER_M = ROLLER_RADIUS_M * 2;
+export const ROLLER_SPACING_M = 0.15;          // 150mm between rollers
+export const ROLLER_Y = BELT_BOTTOM_Y - ROLLER_RADIUS_M - 0.01; // Just below belt
+
+// Frame structure
+export const FRAME_HEIGHT_M = CONVEYOR_HEIGHT_M - BELT_THICKNESS_M - ROLLER_DIAMETER_M;
+export const FRAME_WIDTH_M = 0.06;             // 60mm frame profile
+export const SIDE_GUARD_HEIGHT_M = 0.08;       // 80mm side guards above belt
+export const SIDE_GUARD_Y = BELT_TOP_Y + SIDE_GUARD_HEIGHT_M / 2;
+
+// Support legs
+export const LEG_WIDTH_M = 0.05;               // 50mm square legs
+export const LEG_SPACING_M = 2.0;              // Every 2m
+
+// =========================================================
+// Motor drive
+// =========================================================
+export const MOTOR_WIDTH_M = 0.12;             // 120mm motor body
+export const MOTOR_HEIGHT_M = 0.15;            // 150mm motor height
+export const MOTOR_DEPTH_M = 0.08;             // 80mm motor depth
+export const DRIVE_ROLLER_RADIUS_M = 0.06;     // 60mm drive roller
+
+// =========================================================
+// Zone positions (X axis = along conveyor, Z axis = lateral)
+// =========================================================
+export const ZONES = {
+  /** Zone A - item spawn point (start of conveyor) */
+  A: { x: -4.0, z: 0, label: 'A' },
+  /** Camera/CV detection zone */
+  CAMERA: { x: -1.5, z: 0 },
+  /** Laser measurement zone */
+  LASER: { x: -0.5, z: 0 },
+  /** Gate/diverter position */
+  GATE: { x: 1.5, z: 0 },
+  /** Zone B - main sorter exit (end of main conveyor) */
+  B: { x: 4.0, z: 0, label: 'B' },
+  /** Zone C - oversized items (lateral) */
+  C: { x: 2.0, z: 2.0, label: 'C' },
+  /** Zone D - round items (lateral opposite) */
+  D: { x: 2.0, z: -2.0, label: 'D' },
+} as const;
+
+// =========================================================
+// Roll cages (C/D destination bins)
+// =========================================================
+export const ROLL_CAGE = {
+  width: 1.2,   // 1200mm
+  depth: 0.8,   // 800mm
+  height: 0.8,  // 800mm
+};
+
+// =========================================================
+// Item positioning
+// =========================================================
+
+/**
+ * Calculate item Y position so it sits ON the belt surface.
+ * @param itemVisualHeight - Visual height of item mesh in meters
+ * @returns Y position for item center
+ */
+export function getItemYOnBelt(itemVisualHeight: number): number {
+  // Item center = belt top + half item height
+  return BELT_TOP_Y + itemVisualHeight / 2;
+}
+
+/**
+ * Get standard item Y for small/medium items.
+ * Most items are ~0.1-0.3m tall visually.
+ */
+export function getStandardItemY(): number {
+  const averageItemHeight = 0.15; // 150mm average
+  return getItemYOnBelt(averageItemHeight);
+}
+
+// =========================================================
+// Camera rig
+// =========================================================
+export const CAMERA_RIG = {
+  height: 1.2,           // 1.2m overhead frame
+  poleSpacing: 0.6,      // Poles 0.6m apart (outside belt)
+  cameraY: 1.1,          // Camera at 1.1m
+};
+
+// =========================================================
+// Derived constants for legacy compatibility
+// =========================================================
+export const CONVEYOR_POSITIONS = {
+  spawnX: ZONES.A.x,
+  cameraX: ZONES.CAMERA.x,
+  laserX: ZONES.LASER.x,
+  gateX: ZONES.GATE.x,
+  zoneBX: ZONES.B.x,
+  zoneCZ: ZONES.C.z,
+  zoneDZ: ZONES.D.z,
+  beltY: BELT_TOP_Y,
+  itemOffsetY: 0.075, // Half of average item height
+} as const;