feat: add zoom-to-object on double-click (#139)

Double-clicking any star raycasts into the scene and smoothly flies
the camera to 8 units from the hit point over 1.4 s using an
ease-in-out curve. Camera faces the object throughout the animation.

Fixes #139

app.js

@@ -119,6 +119,39 @@ document.addEventListener('mousemove', (e) => {
   mouseY = (e.clientY / window.innerHeight - 0.5) * 2;
 });
 
+// === ZOOM TO OBJECT (double-click to fly) ===
+const raycaster = new THREE.Raycaster();
+raycaster.params.Points.threshold = 3;
+const mouse2D = new THREE.Vector2();
+
+let zoomTarget = null;
+let zoomOrigin = null;
+let zoomLookAt = null;
+let zoomStartTime = 0;
+const ZOOM_DURATION = 1.4;
+
+function easeInOutQuad(t) {
+  return t < 0.5 ? 2 * t * t : -1 + (4 - 2 * t) * t;
+}
+
+renderer.domElement.addEventListener('dblclick', (e) => {
+  mouse2D.x = (e.clientX / window.innerWidth) * 2 - 1;
+  mouse2D.y = -(e.clientY / window.innerHeight) * 2 + 1;
+
+  raycaster.setFromCamera(mouse2D, camera);
+  const intersects = raycaster.intersectObject(stars);
+
+  if (intersects.length > 0) {
+    const hitPoint = intersects[0].point.clone();
+    // Approach from current camera direction, stop 8 units from hit
+    const approach = camera.position.clone().sub(hitPoint).normalize().multiplyScalar(8);
+    zoomOrigin = camera.position.clone();
+    zoomTarget = hitPoint.clone().add(approach);
+    zoomLookAt = hitPoint.clone();
+    zoomStartTime = clock.getElapsedTime();
+  }
+});
+
 // === RESIZE HANDLER ===
 window.addEventListener('resize', () => {
   camera.aspect = window.innerWidth / window.innerHeight;
@@ -146,6 +179,17 @@ function animate() {
   // Subtle pulse on constellation opacity
   constellationLines.material.opacity = 0.12 + Math.sin(elapsed * 0.5) * 0.06;
 
+  // Zoom-to-object animation
+  if (zoomTarget) {
+    const t = Math.min((elapsed - zoomStartTime) / ZOOM_DURATION, 1);
+    const ease = easeInOutQuad(t);
+    camera.position.lerpVectors(zoomOrigin, zoomTarget, ease);
+    camera.lookAt(zoomLookAt);
+    if (t >= 1) {
+      zoomTarget = null;
+    }
+  }
+
   renderer.render(scene, camera);
 }