feat(phases): implement webhooks (6.1), email (7.1), user preferences (7.2)

- Phase 6.1: WebhookConfig model, CRUD router (/api/v1/webhooks, admin-only),
  dispatch_webhook() with HMAC signing; integrated into test validation,
  campaign completion, and MITRE sync job
- Phase 7.1: SMTP email service with send_test_validated_email,
  send_campaign_completed_email, send_new_mitre_techniques_email;
  notify_role_with_email() added to notification_service
- Phase 7.2: notification_preferences and jira_account_id on User model;
  PATCH /users/me/preferences endpoint; Alembic migrations b031phase6 and b032phase7

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/models/user.py

@@ -1,6 +1,6 @@
 import uuid
 from sqlalchemy import Column, String, Boolean, DateTime, func
-from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.dialects.postgresql import UUID, JSONB
 
 from app.database import Base
 
@@ -28,3 +28,5 @@ class User(Base):
     must_change_password = Column(Boolean, default=True)
     created_at = Column(DateTime(timezone=True), server_default=func.now())
     last_login = Column(DateTime, nullable=True)
+    notification_preferences = Column(JSONB, nullable=True, server_default='{"email_on_test_validated": true, "email_on_campaign_completed": true, "email_on_new_mitre_techniques": false, "in_app_all": true}')
+    jira_account_id = Column(String(100), nullable=True)