feat: Group NPC — folders, NPC icons, weapon/ability icons

Folder structure:
- Actors sidebar: Generated NPCs > [Type] (e.g. Generated NPCs > Carrion)
- Folders created automatically if they do not already exist
- Each type gets its own colour-coded subfolder

NPC actor portrait:
- Street Gang / Serial Killer: mystery-man.svg
- Carrion / Serial Killer:     skull.svg
- Monstaret:                   hazard.svg
- Machine:                     daze.svg

Weapon item icons mapped by name:
- Bite/claw/natural:   unarmed-punch-fist.webp
- Acid/spit:           aura.svg
- Rifle/minigun:       rifle-bayonet.webp
- Shotgun:             gun-blunderbuss.webp
- Pistol/SMG/ranged:   gun-pistol-flintlock-metal.webp
- Blunt melee:         club-simple-black.webp
- Blade/knife/sharp:   dagger-straight-sharp.webp

Armor icons: light (<3) vest-simple-leather, heavy (3+) breastplate

Ability icons mapped by keyword (stealth=cowled, acid=aura,
fire=fire, stun/emp=daze, bleed=blood, heal=regen, else=lightning)

system.json

@@ -2,7 +2,7 @@
   "id": "zero-engine",
   "title": "Zero Engine (SLA Industries)",
   "description": "A basic game system for SLA Industries using the Zero Engine rules.",
-  "version": "1.5.5",
+  "version": "1.5.6",
   "compatibility": {
     "minimum": 13,
     "verified": "14.359"