- Play thunder claps on habitable storm strikes, solar-flare SFX on red
dwarf flare onset, and solar-buzz on binary light-trade midpoint
crossings, all via the shared Sfx voice (new playSfxOneOfOn helper)
- Add per-context music volume overrides (music.volumes) so each context
can deviate from the global mix; menu ships at full volume
- Expand surface music frames to cover rocky and ice worlds (frames 6-11)
- Teardown per-system effect layers on scene restart (jump) so a previous
system's storm doesn't keep striking and playing thunder in the new one
- Update planets.png sheet, add gasgiant-03/rocky-01/rocky-02 tracks, and
register the new SFX assets in GameScene preload
