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/delete.go

@@ -0,0 +1,59 @@
+package cli
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/urfave/cli/v3"
+
+	"git.morlana.online/f.weber/vault-tui/internal/vault"
+)
+
+func deleteCommand() *cli.Command {
+	return &cli.Command{
+		Name:      "delete",
+		Usage:     "delete a secret (soft-delete for KV v2; irreversible for KV v1/cubbyhole)",
+		ArgsUsage: "<path>",
+		Flags: []cli.Flag{
+			&cli.BoolFlag{Name: "destroy", Usage: "KV v2: permanently destroy instead of soft-delete (irreversible)"},
+			&cli.BoolFlag{Name: "metadata", Usage: "KV v2: delete all versions and metadata (irreversible)"},
+			&cli.IntSliceFlag{Name: "versions", Usage: "KV v2: specific versions to target (default: current)"},
+		},
+		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 delete <path>")
+			}
+			if _, err := a.EnsureLoggedIn(ctx, cmd.String("token")); err != nil {
+				return err
+			}
+			svc := a.Service()
+			if svc.ReadOnly {
+				return fmt.Errorf("refusing to delete: vault-tui is in read-only mode (pass --write to override)")
+			}
+			mount, rel, err := splitMountPath(ctx, svc, cmd.Args().First())
+			if err != nil {
+				return err
+			}
+
+			op := vault.OpSoftDelete
+			if mount.Kind != vault.EngineKVv2 {
+				op = vault.OpDeleteV1
+			} else if cmd.Bool("metadata") {
+				op = vault.OpDeleteMetadata
+			} else if cmd.Bool("destroy") {
+				op = vault.OpDestroy
+			}
+
+			ack, err := svc.KV.Delete(ctx, mount, rel, op, cmd.IntSlice("versions"))
+			if err != nil {
+				return err
+			}
+			fmt.Printf("deleted %s (op=%v)\n", ack.Path, ack.Op)
+			return nil
+		},
+	}
+}