pickups, native build, enemy/bullet/stage overhaul

- Add pickup system (bomb, spread, rapid, shield) with new sprites
- Replace Docker build with native SGDK compile via m68k-elf-gcc
- Rework enemy spawning, homing math, boss HP/number globals
- Expand chrome: score popups, minimap, pause/game over improvements
- Overhaul stage generation with threat-point system
- Add explosion sprites, shield sprite, powerup sprite
- Add tools/ for sprite downscaling utilities

res/resources.res

@@ -21,7 +21,8 @@ IMAGE door "door.png" NONE NONE
 SPRITE momoyoSprite "momoyo.png" 6 6 NONE 0
 
 SPRITE bulletsSprite "bullets.png" 2 2 NONE 0
-SPRITE pBulletSprite "pbullet.png" 4 4 NONE 0
+SPRITE explosionsSprite "explosions.png" 4 4 NONE 0
+SPRITE explosionBigSprite "explosionsbig.png" 8 8 NONE 0
 
 SPRITE fairySprite "fairy2.png" 4 4 NONE 8
 SPRITE eyeBigSprite "eyebig.png" 4 4 NONE 0
@@ -32,6 +33,8 @@ SPRITE boss4Sprite "enemies/boss4.png" 6 6 NONE 0
 SPRITE treasureSprite "treasure.png" 4 4 NONE 0
 
 SPRITE bonusObjSprite "bonus.png" 2 2 NONE 0
+SPRITE pickupSprite "powerup.png" 2 2 NONE 0
+SPRITE shieldSprite "shield.png" 6 6 NONE 0
 TILESET bonusBgTiles "bonusbg.png" NONE
 
 IMAGE mapIndicator "mapindicator.png" NONE NONE