feat: 3 scene rendering setup

apps/viewer/src/viewerGalaxyLayer.ts

@@ -0,0 +1,37 @@
+import * as THREE from "three";
+import type { Selectable } from "./viewerTypes";
+
+/**
+ * Galaxy rendering layer — the galaxy map.
+ * Scene coordinate unit: display-unit (light-year scale).
+ * Only visible in galaxy POV, rendered on top of the universe backdrop.
+ * Contains star dots and shell reticles for each system.
+ */
+export class GalaxyLayer {
+  readonly scene = new THREE.Scene();
+  readonly camera = new THREE.PerspectiveCamera(50, 1, 0.1, 600000);
+
+  /** Star dots and shell reticles, one per system. */
+  readonly systemGroup = new THREE.Group();
+
+  readonly selectableTargets = new Map<THREE.Object3D, Selectable>();
+
+  constructor() {
+    this.scene.fog = new THREE.FogExp2(0x040912, 0.000035);
+    this.scene.add(new THREE.AmbientLight(0x90a6c0, 0.55));
+    const keyLight = new THREE.DirectionalLight(0xdcecff, 1.3);
+    keyLight.position.set(1000, 1200, 800);
+    this.scene.add(keyLight);
+    this.scene.add(this.systemGroup);
+  }
+
+  updateCamera(focus: THREE.Vector3, orbitOffset: THREE.Vector3) {
+    this.camera.position.copy(focus).add(orbitOffset);
+    this.camera.lookAt(focus);
+  }
+
+  onResize(aspect: number) {
+    this.camera.aspect = aspect;
+    this.camera.updateProjectionMatrix();
+  }
+}