feat(vault-tui): implement KV client and service for managing secrets

- Added internal/vault/client.go for creating a Vault client with configuration settings.
- Introduced internal/vault/errors.go to classify Vault API errors for better UI handling.
- Created internal/vault/kv.go to manage KV secrets, including listing, reading, writing, and deleting operations.
- Implemented internal/vault/mounts.go to list and describe secret engine mounts.
- Developed internal/vault/service.go to provide a unified entry point for Vault operations.
- Added internal/vault/kv_test.go for comprehensive testing of KV operations.
- Introduced internal/ui/toast.go for transient notifications in the UI.
- Added renovate.json for dependency management and updates.

internal/cli/list.go

@@ -0,0 +1,50 @@
+package cli
+
+import (
+	"context"
+	"fmt"
+	"os"
+
+	"github.com/urfave/cli/v3"
+)
+
+func listCommand() *cli.Command {
+	return &cli.Command{
+		Name:      "list",
+		Aliases:   []string{"ls"},
+		Usage:     "list secrets under a path (e.g. `vault-tui list secret/team/`)",
+		ArgsUsage: "<path>",
+		Flags:     []cli.Flag{&cli.BoolFlag{Name: "json"}},
+		Action: func(ctx context.Context, cmd *cli.Command) error {
+			a, err := appFrom(ctx)
+			if err != nil {
+				return err
+			}
+			if cmd.Args().Len() == 0 {
+				return fmt.Errorf("usage: vault-tui list <path>")
+			}
+			if _, err := a.EnsureLoggedIn(ctx, cmd.String("token")); err != nil {
+				return err
+			}
+			svc := a.Service()
+			mount, rel, err := splitMountPath(ctx, svc, cmd.Args().First())
+			if err != nil {
+				return err
+			}
+			l, err := svc.KV.List(ctx, mount, rel)
+			if err != nil {
+				return err
+			}
+			if cmd.Bool("json") {
+				return printJSON(os.Stdout, l)
+			}
+			for _, d := range l.Dirs {
+				fmt.Println(d)
+			}
+			for _, f := range l.Leaves {
+				fmt.Println(f)
+			}
+			return nil
+		},
+	}
+}