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/alembic/versions/b031_phase6_webhooks.py

@@ -0,0 +1,32 @@
+"""Phase 6.1: webhook_configs table.
+
+Revision ID: b031phase6
+Revises: b030phase5
+"""
+from typing import Sequence, Union
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+from alembic import op
+
+revision: str = "b031phase6"
+down_revision: Union[str, None] = "b030phase5"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+def upgrade() -> None:
+    op.create_table(
+        "webhook_configs",
+        sa.Column("id", postgresql.UUID(as_uuid=True), primary_key=True),
+        sa.Column("name", sa.String(200), nullable=False),
+        sa.Column("url", sa.Text, nullable=False),
+        sa.Column("secret", sa.String(256), nullable=True),
+        sa.Column("events", postgresql.JSONB, nullable=False, server_default="[]"),
+        sa.Column("is_active", sa.Boolean, nullable=False, server_default="true"),
+        sa.Column("created_by", postgresql.UUID(as_uuid=True), sa.ForeignKey("users.id", ondelete="SET NULL"), nullable=True),
+        sa.Column("last_triggered_at", sa.DateTime, nullable=True),
+        sa.Column("failure_count", sa.Integer, nullable=False, server_default="0"),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now()),
+    )
+
+def downgrade() -> None:
+    op.drop_table("webhook_configs")