fix: boto3 1.35+ Garage S3 checksum regression

Same fix as comfyui: request_checksum_calculation=when_required.

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

server.py

@@ -38,7 +38,11 @@ def _s3():
         aws_access_key_id=ACCESS_KEY,
         aws_secret_access_key=SECRET_KEY,
         region_name="garage",
-        config=Config(signature_version="s3v4"),
+        config=Config(
+            signature_version="s3v4",
+            request_checksum_calculation="when_required",
+            response_checksum_validation="when_required",
+        ),
     )