Users may not realize that task notifications are disabled by default.To improve awareness, we show a warning alert on the Tasks page when alltask notifications are disabled.**Alert visibility logic:**- Shows when **all** task notification templates (Task Working, TaskIdle, Task Completed, Task Failed) are disabled- Can be dismissed by the user, which stores the dismissal in the userpreferences API- If the user later enables any task notification in Account Settings,the dismissal state is cleared so the alert will show again if theydisable all notifications in the future<img width="2980" height="1588" alt="Screenshot 2025-11-25 at 17 48 17"src="https://github.com/user-attachments/assets/316bf097-d9d2-4489-bc16-2987ba45f45c"/>- Added a warning alert to the Tasks page when all task notificationsare disabled- Introduced new `/users/{user}/preferences` endpoint to manage userpreferences (stored in `user_configs` table)- Alert is dismissible and stores the dismissal state via the new userpreferences API endpoint- Enabling any task notification in Account Settings clears thedismissal state via the preferences API- Added comprehensive Storybook stories for both TasksPage andNotificationsPage to test all alert visibility states and interactionsCloses:coder/internal#1089(cherry picked from commitf8d9a80)