feat(server-folders): support mergeGuildId on folder create IPC

When two guilds are merged via drag, assign both servers to the newly created folder in one create-server-folder handler pass.

Co-authored-by: Cursor <[email protected]>

index.js

@@ -1454,6 +1454,9 @@ async function dispatchUiMessage (platform, msg, hooks = {}) {
     if (msg.initialGuildId && folder?.id) {
       await platform.assignGuildToFolder(msg.initialGuildId, folder.id)
     }
+    if (msg.mergeGuildId && folder?.id) {
+      await platform.assignGuildToFolder(msg.mergeGuildId, folder.id)
+    }
     pushState()
     send({
       type: 'server-folder-created',