fix(proxy): wire games root into asset routes

apps/proxy/src/config.ts

@@ -0,0 +1,12 @@
+/**
+ * Runtime config for the proxy. `GAMES_ROOT` is set at startup (from env or a
+ * default) and read by the asset/trace routes to serve local game assets. It's
+ * a module-level value because the node-server adapter injects its own
+ * `HttpBindings` as the Hono env, not custom bindings.
+ */
+export let GAMES_ROOT: string | undefined;
+
+/** Set the games root at startup. */
+export function setGamesRoot(root: string | undefined): void {
+  GAMES_ROOT = root;
+}