Item system overhaul: rarity bands, per-item caps, source pools + 14 new passives

- Add ITEM_RARITY (common/uncommon/rare/legendary) with per-item tier caps
- Weighted pools per source: elites favour common, item rooms uncommon,
  bosses rare/legendary; legendaries are boss-exclusive; capped items excluded
- Rarity-weighted powerScore so deep common stacks inflate difficulty less
- Differentiate duplicates: Grafted Trigger, Crow Bait, Hollow Bones, Twin Hearts
- 14 new clean passives incl. Chill Gland (activates slowOnHit) and Hooked Sinew
  (activates magnetPull); revive magnetPull in pickups
- Rarity-tinted pedestal glow + nameplates, rarity-sorted HUD implant tray,
  dynamic help implant pages (8 -> 9)
- Generate 14 item icons via gen_assets.py; bump asset cache to v=38
- Update smoke tests for 60 items, per-item caps, pools, weighted power

js/hud.js

@@ -109,7 +109,9 @@ function drawHUD(ctx) {
     ctx.fillText(holsterEmpty ? 'NEEDS AMMO' : Math.ceil(p.holstered.ammo) + ' AMMO', 289, 125 + vOff);
   }
 
-  const allItemEntries = Object.entries(p.items);
+  const rarityRank = { legendary: 0, rare: 1, uncommon: 2, common: 3 };
+  const allItemEntries = Object.entries(p.items).sort((a, b) =>
+    (rarityRank[ITEMS[a[0]].rarity] - rarityRank[ITEMS[b[0]].rarity]) || (b[1] - a[1]));
   const maxVisibleItems = allItemEntries.length > 24 ? 23 : 24;
   const itemEntries = allItemEntries.slice(0, maxVisibleItems);
   if (itemEntries.length) {