feat(ui-flow): handle reorder-categories IPC

Route category drag-reorder from the desktop UI to the platform layer.

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

index.js

@@ -751,6 +751,11 @@ async function dispatchUiMessage (platform, msg, hooks = {}) {
     pushState()
     return true
   }
+  if (t === 'reorder-categories') {
+    await platform.reorderCategories({ categoryIds: msg.categoryIds || [] })
+    pushState()
+    return true
+  }
   if (t === 'toggle-reaction') {
     await platform.toggleReaction(msg.messageId, msg.emoji)
     pushState()