fix(filer): update hard link ctime when nlink changes on unlink (#9018)

* fix(filer): update hard link ctime when nlink changes on unlink

When a hard link is unlinked, POSIX requires that the remaining links'
ctime is updated because the inode's nlink count changed. The filer's
DeleteHardLink() decremented the counter in the KV store but did not
update the ctime field.

Set ctime to time.Now() on the KV entry before writing it back when
the hard link counter is decremented but still > 0.

Remove tests/unlink/00.t from known_failures.txt (all 112 subtests
now pass).

* style: use time.Now().UTC() for ctime in DeleteHardLink

test/pjdfstest/known_failures.txt

@@ -38,12 +38,9 @@ tests/unlink/02.t
 tests/unlink/03.t
 
 # ── Hard link nlink/ctime tracking (requires filer changes) ────────────
-# The filer does not update ctime on remaining hard link entries when one
-# link is removed, and nlink counts are not correctly maintained across
-# rename operations.
+# nlink counts are not correctly maintained across rename operations.
 tests/rename/23.t
 tests/rename/24.t
-tests/unlink/00.t
 
 # ── Parent directory mtime/ctime on deferred file create ───────────────
 # When file creation is deferred (not flushed to filer immediately),

weed/filer/filerstore_hardlink.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"time"
 
 	"github.com/seaweedfs/seaweedfs/weed/glog"
 	"github.com/seaweedfs/seaweedfs/weed/pb/filer_pb"
@@ -113,6 +114,9 @@ func (fsw *FilerStoreWrapper) DeleteHardLink(ctx context.Context, hardLinkId Har
 		return fsw.KvDelete(ctx, key)
 	}
 
+	// POSIX: update ctime when nlink changes (a hard link was removed).
+	entry.Attr.Ctime = time.Now().UTC()
+
 	newBlob, encodeErr := entry.EncodeAttributesAndChunks()
 	if encodeErr != nil {
 		return encodeErr