fix: ollie-9p write/rdwr propagate clunk errors

The 9P protocol returns write handler errors via Rclunk, not Rwrite.
cmdWrite and cmdRdwr were using defer fid.Close() which discarded the
error. Now they check fid.Close() return value and exit non-zero on
failure, allowing the GUI to detect rename errors.

cmd/ollie-9p/main.go

@@ -193,10 +193,15 @@ func cmdWrite(path string) {
 	if err != nil {
 		fatalf("open %s: %v", path, err)
 	}
-	defer fid.Close()
 	if _, err := io.Copy(fid, os.Stdin); err != nil {
+		fid.Close()
 		fatalf("write %s: %v", path, err)
 	}
+	// Close flushes buffered writes; errors (e.g., validation failures)
+	// are returned via Rclunk.
+	if err := fid.Close(); err != nil {
+		fatalf("close %s: %v", path, err)
+	}
 }
 
 func cmdRdwr(path string) {
@@ -205,24 +210,30 @@ func cmdRdwr(path string) {
 	if err != nil {
 		fatalf("open %s: %v", path, err)
 	}
-	defer fid.Close()
 
 	// Write stdin
 	data, err := io.ReadAll(os.Stdin)
 	if err != nil {
+		fid.Close()
 		fatalf("read stdin: %v", err)
 	}
 	if _, err := fid.Write(data); err != nil {
+		fid.Close()
 		fatalf("write %s: %v", path, err)
 	}
 
 	// Seek back to 0 and read response
 	if _, err := fid.Seek(0, 0); err != nil {
+		fid.Close()
 		fatalf("seek %s: %v", path, err)
 	}
 	if _, err := io.Copy(os.Stdout, fid); err != nil {
+		fid.Close()
 		fatalf("read %s: %v", path, err)
 	}
+	if err := fid.Close(); err != nil {
+		fatalf("close %s: %v", path, err)
+	}
 }
 
 func cmdStat(path string) {