Implement Smart Notifications

[Shredder401k]

Type: Feature
Priority: Medium
Labels: feature, notifications

Description:
Add intelligent notification system with preferences.

Features:

• Channel selection (email, SMS, push)
• Notification grouping
• Smart frequency control
• Quiet hours
• Priority levels

Acceptance Criteria:

• Multi-channel notifications
• User preferences respected
• Notification analytics
• All CI/CD checks must pass

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