Replace simple circle graphics with sprite-based enemies using a shared spritesheet. This change introduces:
- A `frameOffset` config to select specific enemy types from the spritesheet.
- An animation system for walking cycles (2-frame loop) and a static death frame.
- A refined hitbox setup using `setCircle` centered within 48x48 frames.
- A visual death sequence: stop movement, show death frame, wait 2s, then fade out.
- HP bar positioning adjusted to account for the new sprite height.
Additionally:
- Added a new `Reticle` UI component that tracks the mouse cursor with rotating rings and hides the OS cursor.
- Updated `GameScene` to load the enemy spritesheet and manage the reticle lifecycle.
Brian Fertig