feat: implement debug node

Closes #39

app/src/lib/result-viewer/debug.ts

@@ -0,0 +1,90 @@
+import { splitNestedArray } from '@nodarium/utils';
+import {
+  BufferGeometry,
+  type Group,
+  InstancedMesh,
+  Line,
+  LineBasicMaterial,
+  Matrix4,
+  MeshBasicMaterial,
+  SphereGeometry,
+  Vector3
+} from 'three';
+
+function writePath(scene: Group, data: Int32Array): Vector3[] {
+  const positions: Vector3[] = [];
+  const f32 = new Float32Array(data.buffer);
+
+  for (let i = 2; i + 2 < f32.length; i += 4) {
+    const vec = new Vector3(f32[i], f32[i + 1], f32[i + 2]);
+    positions.push(vec);
+  }
+
+  // Path line
+  if (positions.length >= 2) {
+    const geometry = new BufferGeometry().setFromPoints(positions);
+    const line = new Line(
+      geometry,
+      new LineBasicMaterial({ color: 0xff0000, depthTest: false })
+    );
+    scene.add(line);
+  }
+
+  // Instanced spheres at points
+  if (positions.length > 0) {
+    const sphereGeometry = new SphereGeometry(0.05, 8, 8); // keep low-poly
+    const sphereMaterial = new MeshBasicMaterial({
+      color: 0xff0000,
+      depthTest: false
+    });
+
+    const spheres = new InstancedMesh(
+      sphereGeometry,
+      sphereMaterial,
+      positions.length
+    );
+
+    const matrix = new Matrix4();
+    for (let i = 0; i < positions.length; i++) {
+      matrix.makeTranslation(
+        positions[i].x,
+        positions[i].y,
+        positions[i].z
+      );
+      spheres.setMatrixAt(i, matrix);
+    }
+
+    spheres.instanceMatrix.needsUpdate = true;
+    scene.add(spheres);
+  }
+
+  return positions;
+}
+
+function clearGroup(group: Group) {
+  for (let i = group.children.length - 1; i >= 0; i--) {
+    const child = group.children[i];
+    group.remove(child);
+    // optional but correct: free GPU memory
+    // @ts-expect-error three.js runtime fields
+    child.geometry?.dispose?.();
+    // @ts-expect-error three.js runtime fields
+    child.material?.dispose?.();
+  }
+}
+
+export function updateDebugScene(
+  group: Group,
+  data: Record<number, { type: string; data: Int32Array }>
+) {
+  clearGroup(group);
+  return Object.entries(data || {}).map(([, d]) => {
+    switch (d.type) {
+      case 'path':
+        splitNestedArray(d.data)
+          .forEach(p => writePath(group, p));
+    }
+    // eslint-disable-next-line @typescript-eslint/no-unused-vars
+    return (_g: Group) => {};
+  }).flat();
+}