Fix global placeholders save crashing with non-serializable error

The placeholders:globals:set IPC handler destructured { values } from
its args, but the renderer sends the placeholders object directly,
so values was always undefined and JSON.stringify(undefined) threw.

app/main.js

@@ -485,7 +485,7 @@ function setupIpc() {
     return settings.data;
   });
   h('placeholders:globals:get', () => settings.getGlobalPlaceholders());
-  h('placeholders:globals:set', ({ values }) => settings.setGlobalPlaceholders(values));
+  h('placeholders:globals:set', (values) => settings.setGlobalPlaceholders(values));
 
   // capture
   h('capture:shoot', async ({ guideId, mode, delayMs }) => {