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.

packages/shared/src/types.ts

@@ -31,6 +31,31 @@ export interface TTSObject {
   CustomImage?: {
     ImageURL: string;
     ImageSecondaryURL: string;
+    ImageScalar?: number;
+    WidthScale?: number;
+    CustomTile?: {
+      Type: number;
+      Thickness: number;
+      Stackable: boolean;
+      Stretch: boolean;
+    };
+    CustomToken?: {
+      Thickness: number;
+      MergeDistancePixels: number;
+      StandUp: boolean;
+      Stackable: boolean;
+    };
+  };
+  /** A custom 3D model, e.g. `Custom_Model`, `Custom_Model_Bag`. */
+  CustomMesh?: {
+    MeshURL: string;
+    DiffuseURL: string;
+    NormalURL: string;
+    ColliderURL: string;
+    Convex: boolean;
+    MaterialIndex: number;
+    TypeIndex: number;
+    CastShadows: boolean;
   };
 }