feat(phase-18): add in-app notification system (T-128, T-129)

backend/app/models/notification.py

@@ -0,0 +1,39 @@
+"""Notification model — in-app notifications for user actions."""
+
+import uuid
+from datetime import datetime
+
+from sqlalchemy import Column, String, Text, Boolean, DateTime, ForeignKey, Index
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import relationship
+
+from app.database import Base
+
+
+class Notification(Base):
+    """
+    In-app notification for alerting users when they need to act.
+
+    Types include: test_assigned, validation_needed, test_rejected,
+    test_validated, test_state_changed, etc.
+    """
+    __tablename__ = "notifications"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    user_id = Column(UUID(as_uuid=True), ForeignKey("users.id"), nullable=False)
+    type = Column(String, nullable=False)
+    title = Column(String, nullable=False)
+    message = Column(Text, nullable=True)
+    entity_type = Column(String, nullable=True)
+    entity_id = Column(UUID(as_uuid=True), nullable=True)
+    read = Column(Boolean, default=False)
+    created_at = Column(DateTime, default=datetime.utcnow)
+
+    # Relationships
+    user = relationship("User")
+
+    __table_args__ = (
+        Index("ix_notifications_user_id", "user_id"),
+        Index("ix_notifications_read", "read"),
+        Index("ix_notifications_created_at", "created_at"),
+    )