perf(spectrum): smooth visual switching (0.3.2)

[jamiesun]

Summary

• retain initialized Three.js spectrum scenes and canvases across style switches
• preload lazy WebGL modules during idle time and reuse render sizes to avoid interaction-path reallocations
• use English spectrum labels and lower Voyage engine-particle opacity to 30%
• bump the desktop application version to 0.3.2

Validation

• npm run check
• npm test
• npm run build