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.

docs/architecture.md

@@ -45,8 +45,8 @@ apps/web ──► apps/proxy ──► packages/tts ──► packages/shared
 
 ### Edges
 
-- **`apps/web` → `apps/proxy`** — calls `/search`, `/items/:id`, and
-  `/items/:id/file` over HTTP.
+- **`apps/web` → `apps/proxy`** — calls `/search`, `/items/:id`,
+  `/items/:id/file`, and `/asset` (CORS-safe asset proxy) over HTTP.
 - **`apps/web` → `packages/extract`** — uses `buildTree` / `collectRefs`
   to analyze a loaded `TTSMod` in the browser (tree sidebar + asset refs).
 - **`apps/proxy` → `packages/tts`** — calls `fetchMod` / `getFileName` to serve
@@ -82,6 +82,10 @@ apps/web ──► apps/proxy ──► packages/tts ──► packages/shared
 | `bson`             | BSON deserialization of TTS save files    | `packages/tts`     |
 | `cheerio`          | Workshop browse page scraping             | `apps/proxy`       |
 | `zod`              | Runtime validation                        | `apps/proxy`, `packages/shared` |
+| `three`            | 3D rendering                              | `apps/web`         |
+| `@react-three/fiber` | React renderer for three.js             | `apps/web`         |
+| `@react-three/drei`  | three.js helpers (controls, textures)   | `apps/web`         |
+| `@react-three/postprocessing` | Post-processing effects    | `apps/web`         |
 
 ### Runtime constraints
 
@@ -103,7 +107,7 @@ apps/web ──► apps/proxy ──► packages/tts ──► packages/shared
 
 - The proxy runs as a single Node process via `@hono/node-server`.
 - `apps/web` is a static Vite build served separately; during development it
-  proxies `/search`, `/items`, and `/health` to the proxy.
+  proxies `/search`, `/items`, `/health`, and `/asset` to the proxy.
 - `packages/extract` is published/consumed as a plain ESM module usable from a
   browser bundle or Node.
 - No shared state between requests; each request fetches fresh.