Task 554: Fix moon positions in 3D viewer scenes (TDD)

Status: DONE

Summary

Fixed Saturn/Enceladus and Uranus/Titania appearing at the same position in 3D viewer.

Both moons had hardcoded x: 0, y: 0, z: 0 (identical to their parent planet).

Root Cause

• prepareSaturnScene and prepareUranusScene set moon coordinates to (0,0,0)
• The orbitRadius property was only used by the renderer for orbit circle drawing
• Moon sphere position was never computed from orbitRadius

Fix (data layer, TDD)

1. Added LOCAL_SCENE_SCALE = 50,000 export (matching renderer's km→scene conversion)
2. Compute moon position at 45° on orbit: x = (orbitRadius/50000) * cos(π/4), same for y
3. Enceladus: 238,020 km → ~4.76 scene units from Saturn
4. Titania: 436,300 km → ~8.73 scene units from Uranus

Tests added (6 new)

• orbital-3d-viewer-data.test.ts: Enceladus not at Saturn position, Enceladus at correct distance (×2 scenes)
• orbital-3d-viewer-data.test.ts: Titania not at Uranus position, Titania at correct distance (×2 scenes)
• orbital-3d-viewer.test.ts: Enceladus not at Saturn position (real data)
• orbital-3d-viewer.test.ts: Titania not at Uranus position (real data)

Files changed

• ts/src/orbital-3d-viewer-data.ts — export LOCAL_SCENE_SCALE, compute moon positions
• ts/src/orbital-3d-viewer-data.test.ts — 4 new tests (24→28)
• ts/src/orbital-3d-viewer.test.ts — 2 new tests (41→43)
• ts/examples/orbital-3d.html — matching fix for example page

Impact

• Stats: 4,021 TS tests
• Human directive phase 29 item (4) resolved