feat: add file serving endpoint GET /api/documents/{id}/file

Returns original document file from NAS. Fixes 404 on PDF/image
viewer in frontend. Updated frontend iframe/img src to match.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/api/documents.py

@@ -6,6 +6,7 @@ from pathlib import Path
 from typing import Annotated
 
 from fastapi import APIRouter, Depends, HTTPException, Query, UploadFile, status
+from fastapi.responses import FileResponse
 from pydantic import BaseModel
 from sqlalchemy import func, select
 from sqlalchemy.ext.asyncio import AsyncSession
@@ -160,6 +161,28 @@ async def get_document(
     return DocumentResponse.model_validate(doc)
 
 
+@router.get("/{doc_id}/file")
+async def get_document_file(
+    doc_id: int,
+    user: Annotated[User, Depends(get_current_user)],
+    session: Annotated[AsyncSession, Depends(get_session)],
+):
+    """문서 원본 파일 서빙"""
+    doc = await session.get(Document, doc_id)
+    if not doc:
+        raise HTTPException(status_code=404, detail="문서를 찾을 수 없습니다")
+
+    file_path = Path(settings.nas_mount_path) / doc.file_path
+    if not file_path.exists():
+        raise HTTPException(status_code=404, detail="파일을 찾을 수 없습니다")
+
+    return FileResponse(
+        path=str(file_path),
+        filename=file_path.name,
+        media_type=None,  # 자동 감지
+    )
+
+
 @router.post("/", response_model=DocumentResponse, status_code=201)
 async def upload_document(
     file: UploadFile,