feat(mailgun): Improve email parsing with enhanced DMARC detection and reprocess functionalityFeat/mailgun email parsing improvements

[sanyo4ever]

Summary

This PR enhances the Mailgun provider to handle DMARC reports and other emails without body content, and adds functionality to reprocess failed email events.

Problem

Mailgun provider was failing to parse DMARC reports and other emails without body content, resulting in errors:

DMARC reports (common automated emails from Google, Microsoft, etc.) have no body text - only subject and ZIP attachments - causing the provider to crash.

Solution

1. Enhanced Email Parsing

DMARC Detection:

• Multi-indicator detection using sender, subject, content-type, and attachments
• Properly classifies DMARC, SPF, and bounce emails

Flexible Message Handling:

• Handles emails without body content
• Extracts message from subject + attachment descriptions
• Multiple fallback levels for robustness

Email Classification:

• Tags emails with email_type metadata (dmarc_report, spf_report, bounce, alert)
• Allows filtering by email type

Configuration Options:

• skip_dmarc_reports (default: false) - Option to skip DMARC reports
• skip_spf_reports (default: false) - Option to skip SPF reports
• handle_emails_without_body (default: true) - Handle emails without body content

2. Error Alert Reprocessing

Backend:

• New endpoint: POST /alerts/event/error/reprocess
• Database helpers: get_error_alerts_to_reprocess(), dismiss_error_alert_by_id()
• Reprocess single or all error alerts
• Auto-dismiss successfully reprocessed alerts

Frontend:

• Added "Reprocess" buttons to Error Alerts Modal
• Loading states and toast notifications
• Detailed success/failure feedback

Use Case:
After deploying code fixes, users can reprocess previously failed events without resending emails.

Changes

Backend

• keep/providers/mailgun_provider/mailgun_provider.py - Enhanced email parsing logic
• keep/api/routes/alerts.py - Reprocess endpoint and imports
• keep/api/core/db.py - Database helper functions
• docs/snippets/providers/mailgun-snippet-autogenerated.mdx - Updated documentation

Frontend

• keep-ui/entities/alerts/model/useAlerts.ts - Reprocess hook function
• keep-ui/features/alerts/alert-error-event-process/ui/alert-error-event-modal.tsx - UI buttons and handlers

Testing

Tested with:

• ✅ DMARC reports from Google (no body, ZIP attachments)
• ✅ Regular monitoring emails with body content
• ✅ Reprocessing error alerts
• ✅ Email classification and metadata

Results:

• ✅ DMARC emails create alerts successfully
• ✅ Message extracted from subject + attachments
• ✅ No parsing errors
• ✅ Reprocess functionality works for both new and old errors
• ✅ Source facet counter updates correctly

Breaking Changes

None - fully backward compatible with existing functionality.

Screenshots

(Optional: Add screenshots of the Error Alerts Modal with Reprocess buttons)

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Fixes: Mailgun DMARC email parsing failures
Related: #5366 (if applicable)

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