fix: bypass js-dos bundleUpdateConfig by providing config + initFs separately

js-dos v8.3.8 calls bundleUpdateConfig which uses libzip WASM to
re-add .jsdos/jsdos.json into the downloaded bundle. This fails on
our bundles (Unable to add .jsdos/jsdos.json into bundle.zip).

Fix: Instead of using { url } option (which triggers bundleUpdateConfig),
fetch the config from a new API endpoint (/api/games/{id}/config) and
pass it directly via { dosboxConf, jsdosConf, initFs }. This bypasses
the broken bundleUpdateConfig entirely.

Changes:
- New GET /api/games/{id}/config endpoint (GameResource + GameService)
- Exposed resolveCdImages/pickBestCdImage as package-private
- Frontend Play.svelte: fetch config + bundle separately, use new API
- Frontend api.js: new getGameConfig() function

frontend/src/lib/api.js

@@ -111,6 +111,16 @@ export function bundleUrl(game) {
   return `/games/${game.bundle_file}`;
 }
 
+/** Get game config (dosbox.conf + jsdos.json) */
+export async function getGameConfig(id) {
+  const res = await fetch(`${BASE}/api/games/${id}/config`);
+  if (!res.ok) {
+    const err = await res.json().catch(() => ({ error: res.statusText }));
+    throw new Error(err.error || `HTTP ${res.status}`);
+  }
+  return res.json();
+}
+
 /** Get game bundle URL for setup mode (runs SETUP.EXE instead) */
 export function setupBundleUrl(game) {
   if (!game) return null;

frontend/src/pages/Play.svelte

@@ -1,5 +1,5 @@
 <script>
-  import { getGame, bundleUrl, setupBundleUrl } from "../lib/api.js";
+  import { getGame, getGameConfig, bundleUrl, setupBundleUrl } from "../lib/api.js";
   import { push } from "../lib/router.js";
 
   let { id } = $props();
@@ -68,9 +68,27 @@
 
     // Start the DOS emulator
     try {
-      const url = isSetup ? setupBundleUrl(game) : bundleUrl(game);
-      if (!url || !window.Dos) throw new Error("Failed to resolve game bundle");
-      dosCI = await window.Dos(dosContainer, { url });
+      if (isSetup) {
+        // Setup mode: use the streaming setup-bundle endpoint
+        const url = setupBundleUrl(game);
+        if (!url || !window.Dos) throw new Error("Failed to resolve game bundle");
+        dosCI = await window.Dos(dosContainer, { url });
+      } else {
+        // Normal mode: fetch config + bundle separately, use dosboxConf + initFs
+        // This bypasses js-dos's bundleUpdateConfig which fails on our bundles
+        const [config, bundleResp] = await Promise.all([
+          getGameConfig(game.id),
+          fetch(bundleUrl(game)),
+        ]);
+        if (!bundleResp.ok) throw new Error("Failed to download game bundle");
+        const bundle = new Uint8Array(await bundleResp.arrayBuffer());
+        const jsdosConf = config.jsdos_conf ? JSON.parse(config.jsdos_conf) : undefined;
+        dosCI = await window.Dos(dosContainer, {
+          dosboxConf: config.dosbox_conf,
+          jsdosConf,
+          initFs: bundle,
+        });
+      }
       running = true;
     } catch (e) {
       error = e.message;