Draw every body in a system on one shared sphere, so returning to the Sun's system is no long task

Each marker built its own 64 by 32 SphereGeometry, and the Sun's system now has 38 of them: the
renderer's constructor took 15 ms, 12 of them building spheres, and with their first upload a
return to the system made a long task of 52 to 70 ms that the base's 18 bodies never did.

Every marker is now the one unit sphere, scaled to its radius, which it keeps in
userData.radiusAu. The shared sphere is never disposed; Saturn's ring is built in the sphere's
own units, since it is the marker's child; keepMarkersLegible reads the stored radius and scales
against the sphere's.

Measured on :4301, eight returns to the Sun's system each (select null, then 0, at 1600x1000):
before, a long task on 3 of 8 (52-57 ms), swapToSystemSpace 13-17 ms and the first render 30-40;
after, no long task on 8 of 8, the swap 2.7-4.4 ms and the first render 20-38. Earth is drawn at
the same 0.656 AU at arrival, and every member shares one geometry.

Tests: one sphere for every marker, each at bodyMarkerRadiusAu of its radius, and not disposed
with its system; Earth held to its 3-pixel floor at the arrival framing, which no test covered.
Guarded mutants, each failing only its named test: a sphere per marker, the shared sphere
disposed, the ring built in AU inside the scaled marker ('picks Saturn through its rings'), and
the legibility scale divided by the body's radius.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/app/features/galaxy-system/system-orbits-renderer.spec.ts

@@ -9,6 +9,7 @@ import { BodyRecord, RotationalElements } from '../../shared/models/body.model';
 import { ExoplanetRecord } from '../../shared/models/exoplanet.model';
 import { SystemOrbitsRenderer } from './system-orbits-renderer';
 import { bodyTexturePath, loadCachedTexture } from '../../shared/rendering/texture-catalog';
+import { bodyMarkerRadiusAu } from './system-framing';
 
 /** The clock's UT date that names a TDB one: TT - UT, which moves by under a second a year, earlier. */
 const utOf = (jdTdb: number): number => jdTdb - ttMinusUtSeconds(jdTdb) / 86400;
@@ -512,6 +513,27 @@ describe('photographs', () => {
   });
 });
 
+describe('markers', () => {
+  it('draws every body on the one sphere, scaled to its radius, and leaves that sphere when a system is left', () => {
+    const records: BodyRecord[] = [2500, 60000].map((radiusKm, index) => ({
+      id: `body-${index}`, systemStarId: 0, name: `Body ${index}`, kind: 'planet', radiusKm, orbitSource: 'test',
+      orbit: { semiMajorAxisAu: 1 + index, eccentricity: 0, inclinationDeg: 0, longitudeOfAscendingNodeDeg: 0, argumentOfPeriapsisDeg: 0, meanAnomalyAtEpochDeg: 0, epochJd: DEFAULT_EPOCH_JD },
+      rates: keplerRates(1 + index, GM_SUN_AU3_PER_DAY2)
+    }));
+    const renderer = new SystemOrbitsRenderer(records, [exoplanet({ radiusEarth: 1.1 })], undefined, 1);
+    const meshes = renderer.members.map((member) => member.marker as THREE.Mesh);
+    expect(new Set(meshes.map((mesh) => mesh.geometry)).size).toBe(1);
+    [2500, 60000, 1.1 * 6371].forEach((radiusKm, index) => {
+      const sphere = meshes[index].geometry as THREE.SphereGeometry;
+      expect(meshes[index].scale.x * sphere.parameters.radius).toBeCloseTo(bodyMarkerRadiusAu(radiusKm), 12);
+    });
+    const disposed = vi.fn();
+    meshes[0].geometry.addEventListener('dispose', disposed);
+    renderer.dispose();
+    expect(disposed).not.toHaveBeenCalled();
+  });
+});
+
 describe('derived surfaces', () => {
   const maps = (renderer: SystemOrbitsRenderer): Array<THREE.Texture | null> =>
     renderer.members.map((member) => ((member.marker as THREE.Mesh).material as THREE.MeshStandardMaterial).map);
@@ -553,7 +575,7 @@ describe('derived surfaces', () => {
 describe('exoplanet size without a measured radius', () => {
   const radiusOf = (overrides: Partial<ExoplanetRecord>): number => {
     const renderer = new SystemOrbitsRenderer([], [exoplanet(overrides)], undefined, 1);
-    return ((renderer.members[0].marker as THREE.Mesh).geometry as THREE.SphereGeometry).parameters.radius;
+    return renderer.members[0].marker.userData['radiusAu'];
   };
   const EARTH_AU = 6371 / 149597870.7;
 
@@ -769,7 +791,7 @@ describe('solar-system bodies against Horizons', () => {
     const marker = renderer.members.find((member) => member.id === id)!.marker as THREE.Mesh;
     const centre = worldPosition(id);
     const towards = point.clone().sub(centre).normalize();
-    const radius = (marker.geometry as THREE.SphereGeometry).parameters.radius;
+    const radius = marker.userData['radiusAu'];
     const hit = new THREE.Raycaster(centre.clone().addScaledVector(towards, radius * 4), towards.clone().negate()).intersectObject(marker)[0];
     return { eastDeg: (hit.uv!.x - 0.5) * 360, latDeg: (hit.uv!.y - 0.5) * 180 };
   }