fix: rename download_file import to storage_download to avoid shadow

The route handler async def download_file() shadowed the storage import
of the same name, causing the endpoint to call itself recursively.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

features/doc-service/app/routers/documents.py

@@ -29,7 +29,7 @@ from app.schemas.document import (
 from app.schemas.share import DocumentShareCreate, DocumentShareOut, SharedDocumentOut
 from app.services.ai_client import AIServiceError, classify_document
 from app.services.config_reader import load_doc_config
-from app.services.storage import delete_file, download_file, save_upload
+from app.services.storage import delete_file, download_file as storage_download, save_upload
 
 router = APIRouter()
 
@@ -146,7 +146,7 @@ async def process_document(doc_id: str) -> None:
         await db.commit()
 
         try:
-            pdf_bytes = await download_file(doc.storage_key)
+            pdf_bytes = await storage_download(doc.storage_key)
             text = await asyncio.to_thread(_extract_pdf_text, pdf_bytes)
             result = await classify_document(text)
 
@@ -611,7 +611,7 @@ async def download_file(
         raise HTTPException(status_code=404, detail="Document not found")
 
     try:
-        pdf_bytes = await download_file(doc.storage_key)
+        pdf_bytes = await storage_download(doc.storage_key)
     except FileNotFoundError:
         raise HTTPException(status_code=404, detail="File not found in storage")