feat(notifications): add notification preferences and unsubscribe sup…

[No-bodyq]

Description

• add notification preferences persisted per user and notification type
• • add endpoints to fetch and bulk update preferences
• • add signed unsubscribe flow for email notifications
• • enforce mandatory channels for critical notification types
• • initialize defaults when a user is created

Related Issue

Closes #307

Type of Change

• New feature
• - [x] Test

Testing Steps

• npm test -- --runInBand
• • result: 35 suites passed, 203 tests passed

Checklist

• code follows project standards
• - [x] self-review completed
• - [x] tests pass locally
• - [x] documentation update not required

[drips-wave]

@No-bodyq Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

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