fix: don't overwrite Workshop-loaded patch with autoLoad/chiptune

When switching from Workshop to Sandbox after loading a patch,
the Sandbox's useEffect was running autoLoad() which overwrote
the just-loaded patch. Now it skips if modules are already present.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/client/src/App.jsx

@@ -38,11 +38,11 @@ export default function App({ onSwitchToGame, onSwitchToWorkshop }) {
     return unsub;
   }, []);
 
-  // Auto-load on mount, or load chiptune demo if empty
+  // Auto-load on mount, but skip if modules already loaded (e.g. from Workshop)
   useEffect(() => {
+    if (state.modules.length > 0) return; // Already loaded (Workshop, etc.)
     const loaded = autoLoad();
     if (!loaded || state.modules.length === 0) {
-      // Load chiptune demo preset
       deserialize(CHIPTUNE_PRESET);
     }
   }, []);