docs: update LLM guides for models and layout rules

Document new GUIDE.md expectations for src-layer edits and add index
entries for models and shared types. Clarify layout usage, composable
placement, error page conventions, and model/type ownership so future
changes follow the intended layer boundaries.docs: update LLM guides for models and layout rules

Document new GUIDE.md expectations for src-layer edits and add index
entries for models and shared types. Clarify layout usage, composable
placement, error page conventions, and model/type ownership so future
changes follow the intended layer boundaries.

src/services/GUIDE.md

@@ -17,6 +17,14 @@ component/view -> store/composable -> service module -> httpClient -> hooks
 - request option 可接收 `signal`。
 - 錯誤正規化交給既有 error/http hooks 流程。
 
+## 錯誤處理體系
+
+- `error.ts`：定義 `ApiRequestError`（正規化後的錯誤類別）、`CanceledRequestError`（取消請求）、`normalizeError()`（將 ky HTTPError / TimeoutError / DOMException 統一轉為 `ApiRequestError`）。
+- `http-error.ts`：ky `beforeError` hook，將 response body 的錯誤訊息注入 error 物件。
+- `http-toast.ts`：全域 HTTP error toast，依 status code 顯示對應 snackbar。
+
+service module 不需要自行 catch 並處理錯誤，交由 interceptors/hooks 與上層 composable（如 `useApiCall`）處理。
+
 ## ky 注意事項
 
 - 本專案使用 ky，不使用 axios。