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

backend/app/models/webhook_config.py

@@ -0,0 +1,19 @@
+"""WebhookConfig model — outbound HTTP notification endpoints."""
+import uuid
+from datetime import datetime
+from sqlalchemy import Column, String, Boolean, DateTime, Integer, Text, ForeignKey, func
+from sqlalchemy.dialects.postgresql import UUID, JSONB
+from app.database import Base
+
+class WebhookConfig(Base):
+    __tablename__ = "webhook_configs"
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    name = Column(String(200), nullable=False)
+    url = Column(Text, nullable=False)
+    secret = Column(String(256), nullable=True)  # HMAC signature key
+    events = Column(JSONB, nullable=False, server_default="[]")  # list of event types
+    is_active = Column(Boolean, default=True, nullable=False)
+    created_by = Column(UUID(as_uuid=True), ForeignKey("users.id", ondelete="SET NULL"), nullable=True)
+    last_triggered_at = Column(DateTime, nullable=True)
+    failure_count = Column(Integer, default=0, nullable=False)
+    created_at = Column(DateTime(timezone=True), server_default=func.now())