feat(shell): add group management commands (#8993)

* feat(shell): add group management commands

Add weed shell commands for IAM group management:
- s3.group.create -name <group>
- s3.group.delete -name <group>
- s3.group.list
- s3.group.show -name <group>
- s3.group.add-user -group <group> -user <user>
- s3.group.remove-user -group <group> -user <user>

All commands use GetConfiguration/PutConfiguration gRPC pattern,
consistent with existing shell commands like s3.user.list.

* fix: add nil check for Configuration in group shell commands

Guard against nil Configuration response from GetConfiguration
gRPC call to prevent potential panics. (Gemini review)

weed/shell/command_s3_group_remove_user.go

@@ -0,0 +1,82 @@
+package shell
+
+import (
+	"context"
+	"encoding/json"
+	"flag"
+	"fmt"
+	"io"
+	"time"
+
+	"github.com/seaweedfs/seaweedfs/weed/pb"
+	"github.com/seaweedfs/seaweedfs/weed/pb/iam_pb"
+	"google.golang.org/grpc"
+)
+
+func init() {
+	Commands = append(Commands, &commandS3GroupRemoveUser{})
+}
+
+type commandS3GroupRemoveUser struct {
+}
+
+func (c *commandS3GroupRemoveUser) Name() string {
+	return "s3.group.remove-user"
+}
+
+func (c *commandS3GroupRemoveUser) Help() string {
+	return `remove a user from an S3 IAM group
+
+	s3.group.remove-user -group <groupname> -user <username>
+`
+}
+
+func (c *commandS3GroupRemoveUser) HasTag(CommandTag) bool {
+	return false
+}
+
+func (c *commandS3GroupRemoveUser) Do(args []string, commandEnv *CommandEnv, writer io.Writer) error {
+	f := flag.NewFlagSet(c.Name(), flag.ContinueOnError)
+	group := f.String("group", "", "group name")
+	user := f.String("user", "", "user name")
+	if err := f.Parse(args); err != nil {
+		return err
+	}
+	if *group == "" {
+		return fmt.Errorf("-group is required")
+	}
+	if *user == "" {
+		return fmt.Errorf("-user is required")
+	}
+
+	return pb.WithGrpcClient(false, 0, func(conn *grpc.ClientConn) error {
+		client := iam_pb.NewSeaweedIdentityAccessManagementClient(conn)
+		ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+		defer cancel()
+
+		resp, err := client.GetConfiguration(ctx, &iam_pb.GetConfigurationRequest{})
+		if err != nil {
+			return err
+		}
+		cfg := resp.GetConfiguration()
+		if cfg == nil {
+			return fmt.Errorf("no IAM configuration found")
+		}
+
+		for _, g := range cfg.Groups {
+			if g.Name == *group {
+				for i, m := range g.Members {
+					if m == *user {
+						g.Members = append(g.Members[:i], g.Members[i+1:]...)
+						if _, err := client.PutConfiguration(ctx, &iam_pb.PutConfigurationRequest{Configuration: cfg}); err != nil {
+							return err
+						}
+						return json.NewEncoder(writer).Encode(map[string]string{"group": *group, "removed": *user})
+					}
+				}
+				return fmt.Errorf("user %s is not a member of group %s", *user, *group)
+			}
+		}
+		return fmt.Errorf("group %s not found", *group)
+	}, commandEnv.option.FilerAddress.ToGrpcAddress(), false, commandEnv.option.GrpcDialOption)
+}