- Added new `thruster.mp3` asset and loaded it in **BootScene** (`sfx_thruster` key).
- Extended `Player` class:
* Created `thrusterSound` (looping) on construction.
* Play sound while thrust is active and stop when thrust ends.
* Ensure sound stops on player death and is destroyed on cleanup.
- Minor cleanup to stop thruster audio when the player entity is destroyed.
- Implement `AlienShip.explode()` with cyan flash, shrinking spin animation and a shockwave ring.
- Enhance `Player.die()` to flash white, hide the sprite, and spawn shattering shard graphics.
- Introduce `GameScene.spawnImpactSparks()` to create brief yellow spark particles on bullet impacts.
- Update bullet‑asteroid and bullet‑alien collision handling to trigger impact sparks and use the new alien explosion.
- Minor refactor to use the new visual effects for a more polished death sequence.
Brian Fertig