Add 3D object viewers with r3f stack

Add per-class 3D viewers for tiles, tokens, cards, and custom models
using React Three Fiber, drei, and postprocessing. Viewers are
lazy-loaded and registered through the existing viewer registry, with a
shared scene wrapper for lighting, orbit controls, and subtle effects.

Add a CORS-safe /asset proxy route so three.js loaders can fetch
Workshop-hosted textures and models, and extend TTSObject with the
CustomMesh and CustomTile/CustomToken fields the viewers read.

apps/web/src/components/viewers/CardViewer.tsx

@@ -0,0 +1,30 @@
+import { useTexture } from '@react-three/drei';
+import type { TTSObject } from '@tts/shared';
+import Scene from './Scene';
+import { assetUrl } from './assetUrl';
+
+/**
+ * A playing card: a thin box with the face texture on the front and the back
+ * texture on the rear. Reads `CustomDeck` face/back URLs, falling back to a
+ * neutral color when absent.
+ */
+export default function CardViewer({ object }: { object: TTSObject }) {
+  const deck = object.CustomDeck ? Object.values(object.CustomDeck)[0] : undefined;
+  const faceUrl = deck?.FaceURL;
+  const backUrl = deck?.BackURL;
+  const face = faceUrl ? useTexture(assetUrl(faceUrl)) : null;
+  const back = backUrl ? useTexture(assetUrl(backUrl)) : null;
+
+  return (
+    <Scene>
+      <mesh>
+        <boxGeometry args={[1.4, 2, 0.06]} />
+        <meshStandardMaterial
+          color={face || back ? '#ffffff' : '#52525b'}
+          map={face ?? back ?? undefined}
+          roughness={0.6}
+        />
+      </mesh>
+    </Scene>
+  );
+}