Task 557: Add inertial/ship viewpoint switching to 3D viewer

Status: DONE

Summary

Added viewpoint switching between inertial frame (fixed center) and ship frame

(camera follows the ship marker) in the 3D orbital viewer.

Changes

1. Added ViewMode type ("inertial" | "ship") and supportedViewModes to SceneData
2. All 3 scenes now declare support for both view modes
3. Renderer: setViewMode/getViewMode exports, camera tracking in updateTimelineFrame
4. HTML: "慣性/宇宙船" toggle button in timeline controls

How ship-frame works

• Camera target follows ship marker position during animation
• Camera maintains offset (5, 8, 10) from ship for good viewing angle
• Switching back to inertial resets camera to scene center
• User can still drag to rotate/zoom in both modes

Tests added (2 new)

• orbital-3d-viewer-data.test.ts: full-route supports both view modes
• orbital-3d-viewer-data.test.ts: Saturn scene supports both view modes

Files changed

• ts/src/orbital-3d-viewer-data.ts — ViewMode type, supportedViewModes
• ts/src/orbital-3d-viewer-data.test.ts — 2 new tests (33→35)
• ts/src/orbital-3d-viewer.js — setViewMode, getViewMode, ship-frame camera tracking
• ts/examples/orbital-3d.html — view mode button + handler

Impact

• Stats: 4,031 TS tests
• Human directive phase 29 item (3) addressed: viewpoint switching