feat: Add DomainExtractionMessage model for integration seed discovery

[nsportsman]

Summary

Add new message model to trigger automatic domain extraction from integration-discovered assets.

Related Linear Issue

Relates to: CHARIOT-1359 - Added by filter not working for seeds page

This model enables multi-origin seed tracking, which will support proper filtering by discovery source.

Changes

• New Model: DomainExtractionMessage struct with registry integration
• Purpose: Trigger domain extraction after NS1, Okta, Azure AD integrations discover assets
• Interface: Implements registry.Model for automatic code generation

Model Structure

type DomainExtractionMessage struct {
    Username  string            // AWS context and permissions
    JobKey    string            // Job tracking identifier
    Source    string            // Integration source (ns1, okta, azuread-discovery)
    TargetDNS string            // Target domain for filtering
    Config    map[string]string // Job configuration
    CreatedAt string            // Message timestamp
}

Integration

• Registered in tabularium registry for schema generation
• Supports Python client generation via codegen
• Used by Chariot backend domain extraction Lambda

Related PRs

• praetorian-inc/chariot#3549 - Backend domain extraction + Frontend multi-origin UI

Testing

• Model compiles successfully
• Registry registration successful
• Used in backend Lambda implementation
• Tabularium package builds without errors

Documentation

• Design: seeds-domain-import/CONSOLIDATED-ARCHITECTURE.md
• Validation: seeds-domain-import/DEEP-VALIDATION-REPORT.md
• Architecture Analysis: seeds-domain-import/LAMBDA-VS-EC2-ARCHITECTURE-ANALYSIS.md