refactor(web): extract shared runtime monster-artwork lookup

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/src/app/shared/monster-artwork.spec.ts

@@ -0,0 +1,13 @@
+import { runtimeMonsterArtworkPath } from './monster-artwork';
+
+describe('runtimeMonsterArtworkPath', () => {
+  it('returns the optimized JPEG derivative for a known monster artwork path', () => {
+    expect(runtimeMonsterArtworkPath('/images/monsters/ash-rat.png')).toBe(
+      '/images/monsters/runtime/ash-rat-560.jpg',
+    );
+  });
+
+  it('returns undefined for an artwork path with no runtime derivative', () => {
+    expect(runtimeMonsterArtworkPath('/images/enemies/Dawnwolf.png')).toBeUndefined();
+  });
+});