Much simpler undo/redo handling, bugs fixed and less code.

src/main.js

@@ -3,7 +3,7 @@ import './assets/calendar.css'
 import { createApp } from 'vue'
 import { createPinia } from 'pinia'
 import piniaPluginPersistedstate from 'pinia-plugin-persistedstate'
-import { calendarHistory } from '@/plugins/calendarHistory'
+import { history } from '@/plugins/history'
 
 import App from './App.vue'
 
@@ -12,7 +12,7 @@ const app = createApp(App)
 const pinia = createPinia()
 // Order: persistence first so snapshots recorded by undo reflect already-hydrated state
 pinia.use(piniaPluginPersistedstate)
-pinia.use(calendarHistory)
+pinia.use(history)
 app.use(pinia)
 
 app.mount('#app')