NotificationCenterScreen

Compose the modal layout.

Apply ASCII borders and highlight the first row.

Move the cursor up one row (wraps at the top).

Move the cursor down one row (wraps at the bottom).

Drill into the highlighted notification.

Close without firing any action.

Handle a mouse click on a notification row.

Rebuild the row list from a refreshed snapshot.

Preserves cursor position by key when possible; falls back to clamping the previous index into the new bounds. Dismisses the screen with None when the list is empty.