feat(pose_3d): modello reale G1 (URDF + STL meshes) al posto della silhouette finta

Sostituisce torso/head/hips/gambe/spalle primitive in tab Pose 3D con il
modello URDF G1 (g1_body29_hand14), caricato via urdf-loader 0.12.6.

Vendor:
- web/vendor/g1/g1.urdf + 64 mesh STL (~52 MB, copiati da
  G1_API_Server/assets/g1/)
- web/vendor/three/addons/loaders/URDFLoader.js (npm urdf-loader@0.12.6),
  import path adattato a 'three/addons/loaders/STLLoader.js' (importmap
  del sito) e ColladaLoader stubbato (G1 URDF è solo STL)
- web/vendor/three/addons/loaders/URDFClasses.js (companion del loader)

pose_3d.js:
- Aggiunge loadG1Urdf(scene) async che configura loader.loadMeshCb per
  servire le STL dal mount /static/vendor/g1/meshes/
- Best-effort: in caso di errore di parsing/fetch il body non viene
  aggiunto ma la tab continua a funzionare (polsi, UCS, gizmo)

web/pose_3d.js

@@ -4,6 +4,8 @@
 import * as THREE from 'three';
 import { OrbitControls } from 'three/addons/controls/OrbitControls.js';
 import { TransformControls } from 'three/addons/controls/TransformControls.js';
+import { STLLoader } from 'three/addons/loaders/STLLoader.js';
+import URDFLoader from 'three/addons/loaders/URDFLoader.js';
 
 const $ = (id) => document.getElementById(id);
 const POLL_MS = 1000;
@@ -81,6 +83,45 @@ const SHOULDER = {
   left:  new THREE.Vector3(0,  0.20, 0.60),
 };
 
+// ----- URDF loader -----
+// Carica il modello G1 reale a partire dal URDF vendored sotto
+// /static/vendor/g1/. Le mesh STL referenziate nel URDF (path relativi tipo
+// "meshes/pelvis.STL") vengono risolti contro lo stesso prefisso.
+async function loadG1Urdf(scene) {
+  const loader = new URDFLoader();
+  loader.loadMeshCb = function (path, manager, onComplete) {
+    // path arrives like "meshes/pelvis.STL"; resolve to our static path
+    const url = `/static/vendor/g1/${path}`;
+    const stl = new STLLoader(manager);
+    stl.load(
+      url,
+      (geometry) => {
+        const mat = new THREE.MeshStandardMaterial({
+          color: 0x9099a3, metalness: 0.4, roughness: 0.6,
+          transparent: true, opacity: 0.85,
+        });
+        const mesh = new THREE.Mesh(geometry, mat);
+        onComplete(mesh);
+      },
+      undefined,
+      (err) => onComplete(null, err),
+    );
+  };
+  return new Promise((resolve, reject) => {
+    loader.load(
+      '/static/vendor/g1/g1.urdf',
+      (robot) => {
+        // G1 URDF uses Z-up too (Unitree convention) so no rotation needed
+        scene.add(robot);
+        console.log('[pose_3d] G1 URDF caricato:', robot.name || 'g1');
+        resolve(robot);
+      },
+      undefined,
+      (err) => reject(err),
+    );
+  });
+}
+
 // ----- scene init -----
 function initScene() {
   const canvas = $('p3Canvas');
@@ -117,45 +158,12 @@ function initScene() {
   frontArrow.scale.set(0.18, 0.045, 1);  // più largo ma sottile, "etichetta a terra"
   scene.add(frontArrow);
 
-  // Body silhouette: torso + head + legs + shoulders
-  const bodyMat = new THREE.MeshStandardMaterial({
-    color: 0x4a5560, transparent: true, opacity: 0.6,
+  // Modello G1 reale via URDF (best-effort: se il loader fallisce, niente
+  // body — la tab funziona comunque coi soli polsi/UCS).
+  loadG1Urdf(scene).catch((e) => {
+    console.warn('[pose_3d] URDF G1 non caricato:', e.message);
   });
 
-  // Torso: 20cm x 40cm x 50cm, centered at TORSO_POS
-  const torso = new THREE.Mesh(new THREE.BoxGeometry(0.20, 0.40, 0.50), bodyMat);
-  torso.position.copy(TORSO_POS);
-  scene.add(torso);
-
-  // Head: sfera 12cm sopra il torso
-  const head = new THREE.Mesh(
-    new THREE.SphereGeometry(0.09, 24, 16), bodyMat,
-  );
-  head.position.set(TORSO_POS.x, TORSO_POS.y, TORSO_POS.z + 0.25 + 0.09);
-  scene.add(head);
-
-  // Hips (rectangle) just below torso
-  const hips = new THREE.Mesh(new THREE.BoxGeometry(0.22, 0.36, 0.10), bodyMat);
-  hips.position.set(TORSO_POS.x, TORSO_POS.y, TORSO_POS.z - 0.25 - 0.05);
-  scene.add(hips);
-
-  // Gambe: 2 cilindri verticali, da hip a Z=0
-  const legGeom = new THREE.CylinderGeometry(0.06, 0.06, 0.55, 16);
-  for (const ly of [-0.10, 0.10]) {
-    const leg = new THREE.Mesh(legGeom, bodyMat);
-    leg.rotation.x = Math.PI / 2;  // asse cilindro su Z
-    leg.position.set(TORSO_POS.x, TORSO_POS.y + ly, (TORSO_POS.z - 0.30 - 0.275));
-    scene.add(leg);
-  }
-
-  // Spalle: 2 sferette in corrispondenza degli SHOULDER
-  const shoulderGeom = new THREE.SphereGeometry(0.04, 16, 12);
-  for (const side of ['right', 'left']) {
-    const sh = new THREE.Mesh(shoulderGeom, bodyMat);
-    sh.position.copy(SHOULDER[side]);
-    scene.add(sh);
-  }
-
   // Arms
   for (const side of ['right', 'left']) {
     const wrist = makeWristMarker(side === 'right' ? 0x4da3ff : 0xff5e7e);