feat: enterprise notification & task management system

Phase N.1 — Data Model:
- Extend Notification model with category, priority, task fields (status, action,
  assignee, dueDate, completedAt/By), reminder fields (remindAt, recurrence,
  nextRemindAt), and targeting metadata (sourceId, senderId, channel)
- Add NotificationCategory, NotificationPriority, TaskStatus enums
- Add NotificationBroadcast model for group notifications
- Shared types with parseTaskAction()/buildTaskAction() helpers

Phase N.2 — API:
- Extend notification router: listTasks, taskCounts, updateTaskStatus,
  createReminder/update/delete/list, createBroadcast/listBroadcasts,
  createTask, assignTask, delete
- Broadcast targeting: resolve recipients by user/role/project/orgUnit/all
- Task-action registry: approve_vacation, reject_vacation, confirm_assignment
- Reminder scheduler: 60s poll interval, recurring support, catch-up on start
- SSE events: TASK_ASSIGNED, TASK_COMPLETED, TASK_STATUS_CHANGED,
  REMINDER_DUE, BROADCAST_SENT

Phase N.3 — AI Assistant:
- 7 new tools: list_tasks, get_task_detail, update_task_status,
  execute_task_action, create_reminder, create_task_for_user, send_broadcast
- execute_task_action dispatches to task-action registry with per-action
  permission checks, marks tasks as completed by AI

Phase N.4 — Frontend:
- Enhanced NotificationBell with task badge, tabs (All/Tasks/Reminders)
- TaskCard component with priority badges, due dates, action buttons
- ReminderModal for creating/editing personal reminders
- BroadcastModal for targeted group notifications (manager+)
- NotificationCenter full-page with 5 tabs and bulk actions
- TaskWidget dashboard widget showing open tasks
- Admin broadcast management page
- AppShell nav links for Notifications and Broadcasts
- SSE hook handlers for task/reminder events

Phase N.5 — Auto-Tasks:
- Vacation create → APPROVAL tasks for all managers
- Vacation approve/reject → mark approval tasks as DONE
- Demand create → TASK for managers to fill staffing needs

Co-Authored-By: claude-flow <ruv@ruv.net>

packages/shared/src/constants/index.ts

@@ -53,6 +53,11 @@ export const SSE_EVENT_TYPES = {
   ROLE_UPDATED: "role.updated",
   ROLE_DELETED: "role.deleted",
   NOTIFICATION_CREATED: "notification:created",
+  TASK_ASSIGNED: "task.assigned",
+  TASK_COMPLETED: "task.completed",
+  TASK_STATUS_CHANGED: "task.status_changed",
+  REMINDER_DUE: "reminder.due",
+  BROADCAST_SENT: "broadcast.sent",
   PING: "ping",
 } as const;