Implement Mailgun email event tracking with webhook handler and admin integration

[Copilot]

• Create EmailEvent model to track email events from Mailgun webhooks
• Add email tracking fields to Profile model for Mailgun events
• Create mailgun_webhooks.py module to handle Mailgun webhook events
• Add URL endpoint for Mailgun webhook
• Update admin.py to display Mailgun email status
• Add utility function to get email status for Mailgun events
• Create database migration for new fields
• Add tests for Mailgun webhook handling (7 tests, all passing)
• Verify implementation works with existing Mailgun integration (all 209 tests pass)
• Add comprehensive documentation
• Fix linting issues (black, isort, flake8 all pass)

Summary

This PR implements a complete email event tracking system for Mailgun webhooks, mirroring the functionality of PR #569 for SendGrid. The implementation includes:

✅ Webhook handler with HMAC-SHA256 signature verification
✅ EmailEvent model and Profile extensions for tracking metrics
✅ Admin interface integration with color-coded status display
✅ Slack notifications for email events
✅ 7 comprehensive tests (100% pass rate)
✅ Complete documentation in docs/MAILGUN_EMAIL_TRACKING.md
✅ All linting checks passing (black, isort, flake8)

Fixed a minor formatting issue in web/admin.py where there was an extra backslash in the format_html string that was causing black to fail.

Original prompt

implement a simple email tracker similar to this @alphaonelabs/alphaonelabs-education-website/pull/569 however make it for mailgun

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[github-actions]

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[A1L13N]

@copilot Fix lints

[Copilot]

@copilot Fix lints

Fixed in 9a5011c - removed extra backslash in format_html string in web/admin.py. All linting checks now pass (black, isort, flake8).