fix: correct equipment balance and sort items by stat power (#69)

## Summary

Two improvements to the equipment system in one PR:

### Balance fixes (closes #54)

Full equipment audit revealed 9 items with duplicated stats, regressions, or purchasable items weaker than free boss drops:

| Item | Change | Reason |
|---|---|---|
| Void Conduit | 4x → 7x combat | 100M essence sink was equal to a zone-6 boss drop |
| Void Edge | 2.75x → 3.25x combat | Purchasable was weaker than free Celestial Blade (3x) |
| Astral Robe | 2.25x → 2.75x gold | Boss drop was weaker than purchasable Titan's Aegis (2.5x) |
| Philosopher's Stone | 2x → 2.25x click | Duplicated Frost Crystal's click multiplier |
| Eternal Flame | 1.15x → 1.25x gold | Gold regressed vs Philosopher's Stone (1.25x) |
| Celestial Focus | 2.5x → 3x click | 20M essence sink was weaker than free Angel's Halo (2.75x click + 1.3x gold) |
| Abyssal Tome | 3x → 3.75x gold | 50M essence sink was equal to free Heaven's Mantle (3x) |
| Crystal Matrix | 4x → 4.75x gold | 20M crystal sink was equal to free Sinslayer Aegis (4x) |
| Infernal Gem | 3.5x → 4x click | 5M crystal sink was identical to free Prism Eye |

### Equipment sorting (closes #55)

Equipment cards within each slot now render in ascending order of combined bonus power — the sum of all multiplier bonuses — so stronger items always appear further down the list. Hybrid items such as Volcanic Plate sort correctly without needing a per-slot primary stat.

## Test plan

- [ ] All purchasable weapons/armour/trinkets now exceed the stats of the highest free boss drop at their tier
- [ ] No duplicate stat values between adjacent items in the same progression track
- [ ] Equipment cards within each slot render weakest → strongest
- [ ] Hybrid multi-stat items sort sensibly alongside single-stat items
- [ ] Full pipeline green (lint + build + tests at 100% coverage)

✨ This PR was created with help from Hikari~ 🌸

Reviewed-on: #69
Co-authored-by: Hikari <hikari@nhcarrigan.com>
Co-committed-by: Hikari <hikari@nhcarrigan.com>

apps/web/src/components/game/equipmentPanel.tsx

@@ -7,6 +7,7 @@
 /* eslint-disable react/no-multi-comp -- Sub-component is tightly coupled to the panel */
 /* eslint-disable max-lines-per-function -- Complex component with many render paths */
 /* eslint-disable complexity -- Complex component with many conditional render paths */
+/* eslint-disable max-lines -- Equipment panel with set bonus display and sort logic */
 import { type JSX, useState } from "react";
 import { useGame } from "../../context/gameContext.js";
 import { EQUIPMENT_SETS } from "../../data/equipmentSets.js";
@@ -188,6 +189,20 @@ const EquipmentCard = ({
   );
 };
 
+/**
+ * Computes a combined power score for sorting — sum of all bonus multipliers.
+ * Using the sum (rather than a single stat) keeps hybrid items in sensible order.
+ * @param item - The equipment piece whose bonus multipliers are summed.
+ * @returns The combined bonus value.
+ */
+const equipmentPower = (item: Equipment): number => {
+  return (
+    (item.bonus.combatMultiplier ?? 1)
+    + (item.bonus.goldMultiplier ?? 1)
+    + (item.bonus.clickMultiplier ?? 1)
+  );
+};
+
 const slotOrder: Array<EquipmentType> = [ "weapon", "armour", "trinket" ];
 const slotLabel: Record<EquipmentType, string> = {
   armour:  "🛡️ Armour",
@@ -320,6 +335,8 @@ const EquipmentPanel = (): JSX.Element => {
       {slotOrder.map((slotType) => {
         const items = equipment.filter((item) => {
           return item.type === slotType && (showLocked || item.owned);
+        }).sort((a, b) => {
+          return equipmentPower(a) - equipmentPower(b);
         });
         return (
           <div className="equipment-slot-section" key={slotType}>