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/craftingPanel.tsx

@@ -10,6 +10,7 @@ import { type JSX, useState } from "react";
 import { useGame } from "../../context/gameContext.js";
 import { MATERIALS } from "../../data/materials.js";
 import { RECIPES } from "../../data/recipes.js";
+import { cdnImage } from "../../utils/cdn.js";
 import { ZoneSelector } from "./zoneSelector.js";
 
 const bonusLabel: Record<string, string> = {
@@ -105,6 +106,11 @@ const CraftingPanel = (): JSX.Element => {
                     }`}
                     key={material.id}
                   >
+                    <img
+                      alt={material.name}
+                      className="card-thumbnail"
+                      src={cdnImage("materials", material.id)}
+                    />
                     <div className="material-info">
                       <span className="material-name">{material.name}</span>
                       <span className="material-rarity">{material.rarity}</span>
@@ -144,6 +150,11 @@ const CraftingPanel = (): JSX.Element => {
                       : ""}`}
                     key={recipe.id}
                   >
+                    <img
+                      alt={recipe.name}
+                      className="card-thumbnail"
+                      src={cdnImage("recipes", recipe.id)}
+                    />
                     <div className="recipe-info">
                       <h4>{recipe.name}</h4>
                       <p className="recipe-description">{recipe.description}</p>