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/prompt.go

@@ -0,0 +1,57 @@
+package cli
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strings"
+
+	"golang.org/x/term"
+
+	"git.morlana.online/f.weber/vault-tui/internal/auth"
+)
+
+// promptMissing fills in any of m's still-missing required fields by
+// prompting on the controlling TTY. It never blocks when stdin is not a
+// terminal (e.g. CI/pipes) — callers should check IsInteractive first and
+// treat a non-empty Missing() list as a hard error in that case instead of
+// calling this.
+func promptMissing(m auth.Method, creds auth.Credentials) error {
+	missing := auth.Missing(m, creds)
+	if len(missing) == 0 {
+		return nil
+	}
+	reader := bufio.NewReader(os.Stdin)
+	for _, f := range missing {
+		if f.Kind == auth.FieldSecret {
+			v, err := readPassword(f.Label)
+			if err != nil {
+				return err
+			}
+			creds[f.Name] = v
+			continue
+		}
+		fmt.Fprintf(os.Stderr, "%s: ", f.Label)
+		line, err := reader.ReadString('\n')
+		if err != nil {
+			return fmt.Errorf("reading %s: %w", f.Label, err)
+		}
+		creds[f.Name] = strings.TrimSpace(line)
+	}
+	return nil
+}
+
+func readPassword(label string) (string, error) {
+	fmt.Fprintf(os.Stderr, "%s (will be hidden): ", label)
+	b, err := term.ReadPassword(int(os.Stdin.Fd()))
+	fmt.Fprintln(os.Stderr)
+	if err != nil {
+		return "", fmt.Errorf("reading %s: %w", label, err)
+	}
+	return strings.TrimSpace(string(b)), nil
+}
+
+// IsInteractive reports whether stdin is a terminal we can prompt on.
+func IsInteractive() bool {
+	return term.IsTerminal(int(os.Stdin.Fd()))
+}