[Eyablg-ops]

Fixes #13471

What this PR does
Adds a "Mark All as Read" button on the user notifications page. Clicking it marks all unread notifications visible to the current user (GENERAL + account's roles) as read.

Backend

• New POST /webapi/notifications/read/all endpoint (MarkAllNotificationsAsReadAction).
• The action derives the relevant notification target users server-side from the current account's roles (GENERAL always, plus STUDENT/INSTRUCTOR when applicable), consistent with how notifications are shown.
• NotificationsLogic.createReadNotificationsForAllVisible marks newly-read notifications batch-style, skipping ones already marked read, and returns the IDs marked (idempotent; avoids unique-constraint (accountId, notificationId)).

Frontend

• NotificationService.markAllNotificationsAsRead() consumes the endpoint.
• The notifications list adds a "Mark All as Read" button (disabled when there are no unread notifications or while a request is in flight); the returned read notification IDs are applied to the current tabs in place, so no refetch is needed.

Testing

• Java: 3 new logic tests + 4 new action tests (MarkAllNotificationsAsReadActionTest); full backend component suite passes (1082 tests).
• Frontend: new/extended unit tests for the button; checkstyle, PMD, SpotBugs, ESLint, and Prettier all clean.