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/read.go

@@ -0,0 +1,66 @@
+package cli
+
+import (
+	"context"
+	"fmt"
+	"os"
+
+	"github.com/urfave/cli/v3"
+)
+
+func readCommand() *cli.Command {
+	return &cli.Command{
+		Name:      "read",
+		Usage:     "read a secret (e.g. `vault-tui read secret/team/prod/db`)",
+		ArgsUsage: "<path>",
+		Flags: []cli.Flag{
+			&cli.BoolFlag{Name: "json"},
+			&cli.IntFlag{Name: "version", Usage: "KV v2 version to read (default: latest)"},
+			&cli.StringFlag{Name: "field", Usage: "print only this field's raw value"},
+		},
+		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 read <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
+			}
+			sec, err := svc.KV.Read(ctx, mount, rel, int(cmd.Int("version")))
+			if err != nil {
+				return err
+			}
+			if sec == nil {
+				return fmt.Errorf("no secret found at %s", cmd.Args().First())
+			}
+			if field := cmd.String("field"); field != "" {
+				v, ok := sec.Data[field]
+				if !ok {
+					return fmt.Errorf("field %q not present", field)
+				}
+				fmt.Println(v)
+				return nil
+			}
+			if cmd.Bool("json") {
+				return printJSON(os.Stdout, sec)
+			}
+			out := map[string]string{}
+			for k, v := range sec.Data {
+				out[k] = fmt.Sprint(v)
+			}
+			printKV(os.Stdout, out)
+			if sec.Version > 0 {
+				fmt.Printf("\nversion: %d\n", sec.Version)
+			}
+			return nil
+		},
+	}
+}