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

backend/app/schemas/notification.py

@@ -0,0 +1,28 @@
+"""Pydantic schemas for Notification endpoints."""
+
+import uuid
+from datetime import datetime
+
+from pydantic import BaseModel, ConfigDict
+
+
+class NotificationOut(BaseModel):
+    """Notification returned by the API."""
+
+    id: uuid.UUID
+    user_id: uuid.UUID
+    type: str
+    title: str
+    message: str | None = None
+    entity_type: str | None = None
+    entity_id: uuid.UUID | None = None
+    read: bool = False
+    created_at: datetime | None = None
+
+    model_config = ConfigDict(from_attributes=True)
+
+
+class UnreadCountOut(BaseModel):
+    """Simple counter response."""
+
+    unread_count: int