Space Invaders: reclaim off-screen bullets, enforce black playfield, preserve ESC exit

[Copilot]

Space Invaders was retaining bullets after they left the visible area, which unnecessarily grows object count over time. This update tightens runtime cleanup and ensures the game renders on an explicit black canvas while keeping fast keyboard exit behavior intact.

• Memory/runtime cleanup

  • Added per-frame pruning of bullets that move outside the playable viewport.
  • Introduced a named boundary buffer constant to avoid repeated magic numbers and make cleanup bounds explicit.

• Rendering/background behavior

  • Switched the game from transparent mode to an explicit black background.
  • Set both Phaser scene background and canvas element background to black for consistent full-screen presentation.

• Input/exit behavior

  • Retained ESC handling to immediately destroy the Space Invaders game instance and remove its canvas.

const BULLET_CLEANUP_BUFFER = 40;

const bullets = this.si_bullets?.getChildren?.() || [];
bullets.forEach((bullet) => {
  if (!bullet.active) return;
  if (
    bullet.y < -BULLET_CLEANUP_BUFFER ||
    bullet.x < -BULLET_CLEANUP_BUFFER ||
    bullet.x > this.scale.width + BULLET_CLEANUP_BUFFER
  ) {
    bullet.destroy();
  }
});