Add shareware support and spawn correctly for difficulty levels

Signed-off-by: Hans Kokx <hans.d.kokx@gmail.com>

lib/features/weapon/weapon.dart

@@ -30,8 +30,24 @@ abstract class Weapon {
     this.isAutomatic = true,
   });
 
-  int get currentSprite =>
-      state == WeaponState.idle ? idleSprite : fireFrames[frameIndex];
+  int getCurrentSpriteIndex(int maxSprites) {
+    int baseSprite = state == WeaponState.idle
+        ? idleSprite
+        : fireFrames[frameIndex];
+
+    // Retail VSWAP typically has exactly 436 sprites (indices 0 to 435).
+    // The 20 weapon sprites are ALWAYS placed at the very end of the sprite block.
+    // This dynamically aligns the base index to the end of any VSWAP file!
+    int dynamicOffset = 436 - maxSprites;
+    int calculatedIndex = baseSprite - dynamicOffset;
+
+    // Safety check!
+    if (calculatedIndex < 0 || calculatedIndex >= maxSprites) {
+      print("WARNING: Weapon sprite index $calculatedIndex out of bounds!");
+      return 0;
+    }
+    return calculatedIndex;
+  }
 
   void releaseTrigger() {
     _triggerReleased = true;