feat: add SurveyInvite model

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

backend/app/models/survey_invite.py

@@ -0,0 +1,26 @@
+"""Survey invite tracking for FlowPilot research."""
+import secrets
+import uuid
+from datetime import datetime, timezone
+
+from sqlalchemy import Boolean, Column, DateTime, String
+from sqlalchemy.dialects.postgresql import UUID
+
+from app.core.database import Base
+
+
+def _generate_token() -> str:
+    return secrets.token_urlsafe(16)
+
+
+class SurveyInvite(Base):
+    __tablename__ = "survey_invites"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    token = Column(String(32), unique=True, nullable=False, default=_generate_token)
+    recipient_name = Column(String(255), nullable=False)
+    recipient_email = Column(String(255), nullable=True)
+    status = Column(String(20), nullable=False, default="pending")
+    email_sent = Column(Boolean, nullable=False, default=False)
+    created_at = Column(DateTime(timezone=True), default=lambda: datetime.now(timezone.utc), nullable=False)
+    completed_at = Column(DateTime(timezone=True), nullable=True)