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/styles/README.md

@@ -1,3 +1,16 @@
 # Styles
 
-This directory is for configuring the styles of the application.
+`src/styles` 放 Vuetify 與全域樣式設定。
+
+## 目前檔案
+
+- `settings.scss`：Vuetify SASS 設定，目前主要設定全域字型。
+- `themes.ts`：Vuetify theme definitions，供 `src/plugins/vuetify.ts` 使用。
+
+## 使用規則
+
+- Vuetify SASS 變數與全域字型設定放在 `settings.scss`。
+- 新增或調整 Vuetify theme 時，修改 `themes.ts`，並確認 `src/plugins/vuetify.ts` 有使用對應 theme。
+- component 專屬樣式優先寫在該 `.vue` 檔的 `<style scoped>`。
+- 不要把單一 component 的樣式放進 `src/styles`。
+- 不要在 view 或 component 內重複建立 theme 設定。