feat(core): add attachment schemas

app/schemas/attachment.py

@@ -0,0 +1,23 @@
+"""Attachment schemas — response and list."""
+
+from __future__ import annotations
+
+from pydantic import BaseModel
+
+
+class AttachmentResponse(BaseModel):
+    id: str
+    entity_type: str
+    entity_id: str
+    filename: str
+    file_path: str
+    mime_type: str
+    file_size: int
+    uploaded_by: str | None = None
+    created_at: str | None = None
+    updated_at: str | None = None
+
+
+class AttachmentListResponse(BaseModel):
+    items: list[AttachmentResponse]
+    total: int