feat(file-storage): add storage service and metadata schema

surfsense_backend/app/file_storage/schemas.py

@@ -0,0 +1,23 @@
+"""API shapes for document file metadata."""
+
+from __future__ import annotations
+
+from datetime import datetime
+
+from pydantic import BaseModel, ConfigDict
+
+from app.file_storage.persistence.enums import DocumentFileKind
+
+
+class DocumentFileRead(BaseModel):
+    """Lightweight metadata for one stored document file (no bytes)."""
+
+    id: int
+    document_id: int
+    kind: DocumentFileKind
+    original_filename: str
+    mime_type: str | None = None
+    size_bytes: int
+    created_at: datetime
+
+    model_config = ConfigDict(from_attributes=True)