storage: match default Go idx offset width

seaweed-volume/Cargo.toml

@@ -12,8 +12,9 @@ name = "weed-volume"
 path = "src/main.rs"
 
 [features]
-default = ["5bytes"]
-# Enable 5-byte offset mode for 8TB max volume size (matches Go production builds with -tags 5BytesOffset).
+# Match the default Go build: 4-byte offsets unless explicitly built with 5-byte support.
+default = []
+# Enable 5-byte offset mode for 8TB max volume size (matches Go builds with -tags 5BytesOffset).
 # Without this feature, uses 4-byte offsets with 32GB max volume size.
 5bytes = []