feat: integrate art assets across all game panels (#43)

## Summary

- Adds `apps/web/src/utils/cdn.ts` with a `cdnImage(folder, id)` helper that builds URLs from `https://cdn.nhcarrigan.com/elysium/`
- Wires CDN art into all 13 game panels (bosses, quests, adventurers, companions, equipment, upgrades, prestige, transcendence, achievements, explorations, crafting, story, codex)
- Zone selector tabs now display 16:9 zone art thumbnails in place of emoji icons
- Adds a fixed background image at 15% opacity via `body::before`
- Documents the art generation and CDN upload process in `CLAUDE.md` for future expansions

Resolves #15

✨ This PR was created with help from Hikari~ 🌸

Reviewed-on: #43
Co-authored-by: Hikari <hikari@nhcarrigan.com>
Co-committed-by: Hikari <hikari@nhcarrigan.com>

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

@@ -10,6 +10,7 @@
 import { type JSX, useState } from "react";
 import { useGame } from "../../context/gameContext.js";
 import { EQUIPMENT_SETS } from "../../data/equipmentSets.js";
+import { cdnImage } from "../../utils/cdn.js";
 import { LockToggle } from "../ui/lockToggle.js";
 import type { Equipment, EquipmentType } from "@elysium/types";
 
@@ -20,12 +21,6 @@ const rarityLabel: Record<string, string> = {
   rare:      "Rare",
 };
 
-const typeIcon: Record<EquipmentType, string> = {
-  armour:  "🛡️",
-  trinket: "💍",
-  weapon:  "⚔️",
-};
-
 /**
  * Computes a human-readable bonus description for a piece of equipment.
  * @param item - The equipment item.
@@ -128,7 +123,11 @@ const EquipmentCard = ({
     <div
       className={`equipment-card rarity-${item.rarity} ${equippedClass} ${ownedClass}`}
     >
-      <div className="equipment-icon">{typeIcon[item.type]}</div>
+      <img
+        alt={item.name}
+        className="card-thumbnail"
+        src={cdnImage("equipment", item.id)}
+      />
       <div className="equipment-info">
         <div className="equipment-name-row">
           <h3>{item.name}</h3>