feat: Notification Engine v2 (preferences, templates, in-app notifica…

[Babigdk]

Closes #244

🚀 BE-09: Notification Engine v2

Summary

This PR introduces a centralized notification engine supporting multi-channel delivery (email, push, in-app), user preferences, and templated messages.

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✨ Features

🔔 Notification Preferences

• Per-user, per-event configuration
• Channel-level toggles:
  • Email
  • Push
  • In-app

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🧠 Template Engine

• Deterministic rendering using placeholder interpolation
• Standardized templates for:
  • subject
  • title
  • body

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📥 In-App Notifications

• Persistent storage
• Pagination support
• Sorted by latest first

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✅ Read Management

• Mark single notification as read
• Mark all notifications as read

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📡 API Endpoints

Method	Endpoint	Description
GET	/notifications	List notifications (paginated)
POST	/notifications/:id/read	Mark one as read
POST	/notifications/read-all	Mark all as read

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🧪 Testing

• Unit tests updated for service and preferences
• Verified deterministic template rendering

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✅ Acceptance Criteria

• Preferences enable/disable by type/channel
• In-app notifications paginated
• Templates deterministic

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⚠️ Notes

• Default preference fallback = enabled
• Future extension: SMS channel

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📦 Impact

• Improves user engagement
• Enables scalable notification system
• Foundation for future channels

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[Cedarich]

Kindly fix failing build

[Cedarich]

Please check build

[Babigdk]

on it

[Cedarich]

Fix build