feat(notification): Create notification history service with MongoDB model

[coderooz]

Summary

Create the notification history service for storing and querying agent-to-user notifications.

Acceptance Criteria

• Create \src/domains/notification/notification.service.js\
• MongoDB collection:
  otification_history\ with fields: notification_id, urgency, message, agent, project, sound_path, repeat, timestamp, delivered
• CRUD operations: store, query by urgency, query by date range, query by agent
• Follow existing domain service patterns (see \src/domains/memory/memory.service.js)
• Use MongoDB native driver (no Mongoose)

Schema

\\js
{
notification_id: string (uuid),
urgency: 'info' | 'warning' | 'critical',
message: string,
agent: string,
project: string,
sound_path: string,
repeat: number,
timestamp: Date,
delivered: boolean
}
\\

Related

• Milestone: v2.6.0 — Audio Notification System
• Depends on: MongoDB connection (existing)