feat(stores): add Pinia domain stores and update docs

Implement concrete Pinia stores for app UI and domain data instead of
placeholder re-exports, including seeded student records and snackbar state.

Refresh README guidance for components, plugins, and services to document the
current project structure, data flow, and usage conventions.feat(stores): add Pinia domain stores and update docs

Implement concrete Pinia stores for app UI and domain data instead of
placeholder re-exports, including seeded student records and snackbar state.

Refresh README guidance for components, plugins, and services to document the
current project structure, data flow, and usage conventions.

src/stores/messages.ts

@@ -1 +1,30 @@
-export * from './stores/messages'
+import { defineStore } from 'pinia'
+import { computed, ref } from 'vue'
+
+export const useMessageStore = defineStore('messages', () => {
+  const openState = ref(false)
+
+  // 開啟訊息中心 Dialog
+  const open = () => {
+    openState.value = true
+  }
+
+  // 關閉訊息中心 Dialog
+  const close = () => {
+    openState.value = false
+  }
+
+  // 提供 v-model 綁定用的 computed
+  const isOpen = computed({
+    get: () => openState.value,
+    set: (value) => {
+      openState.value = value
+    },
+  })
+
+  return {
+    isOpen,
+    open,
+    close,
+  }
+})