fix(tier): harden reference proof and audit output (#6807)

Validate lifecycle tier references through the tier reference proof path, preserve S3 list CommonPrefix XML compatibility, and make GetObject audit completion use real S3 error status codes.

Co-authored-by: heihutu <heihutu@gmail.com>

crates/s3-client/src/api_s3_datatypes.rs

@@ -396,3 +396,30 @@ impl DeleteMultiObjects {
         })
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::ListBucketV2Result;
+
+    #[test]
+    fn list_bucket_v2_common_prefix_accepts_s3_pascal_case_xml() {
+        let xml = r#"
+            <ListBucketResult>
+                <Name>tier-bucket</Name>
+                <Prefix></Prefix>
+                <KeyCount>1</KeyCount>
+                <MaxKeys>1000</MaxKeys>
+                <Delimiter>/</Delimiter>
+                <IsTruncated>false</IsTruncated>
+                <CommonPrefixes>
+                    <Prefix>tenant-a/</Prefix>
+                </CommonPrefixes>
+            </ListBucketResult>
+        "#;
+
+        let result = quick_xml::de::from_str::<ListBucketV2Result>(xml).expect("S3 list response should decode");
+
+        assert_eq!(result.common_prefixes.len(), 1);
+        assert_eq!(result.common_prefixes[0].prefix, "tenant-a/");
+    }
+}