ink.branchline.listNotifications

List unread notifications for the authenticated viewer. Requires a valid session cookie; responds 401 otherwise. Notifications are derived from indexed records (no separate notification table) and grouped by subject; a group counts as unread when its latestAt is newer than the viewer's stored readAt for that group (see ink.branchline.markNotificationsRead). Three kinds are emitted: 'continuation' (someone grew one of the viewer's buds), 'seedGrant' (someone gave the viewer a seed), and 'bookmarkGrowth' (new buds on a story the viewer bookmarked).