Fix PyPI proxy to use correct storage.store() method

The code was calling storage.store_artifact() which doesn't exist.
Changed to use storage.store() which handles content-addressable
storage with automatic deduplication.

backend/app/pypi_proxy.py

@@ -451,20 +451,14 @@ async def pypi_download_file(
             content = response.content
             content_type = response.headers.get('content-type', 'application/octet-stream')
 
-        # Compute hash
-        sha256 = hashlib.sha256(content).hexdigest()
-        size = len(content)
+        # Store in S3 (computes hash and deduplicates automatically)
+        from io import BytesIO
+        result = storage.store(BytesIO(content))
+        sha256 = result.sha256
+        size = result.size
 
         logger.info(f"PyPI proxy: downloaded {filename}, {size} bytes, sha256={sha256[:12]}")
 
-        # Store in S3
-        from io import BytesIO
-        artifact = storage.store_artifact(
-            file_obj=BytesIO(content),
-            filename=filename,
-            content_type=content_type,
-        )
-
         # Check if artifact already exists
         existing = db.query(Artifact).filter(Artifact.id == sha256).first()
         if existing: