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/output.go

@@ -0,0 +1,47 @@
+package cli
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"sort"
+	"strings"
+)
+
+// printJSON is the shared -format=json path for every headless command.
+func printJSON(w io.Writer, v interface{}) error {
+	enc := json.NewEncoder(w)
+	enc.SetIndent("", "  ")
+	return enc.Encode(v)
+}
+
+// printKV renders a map as an aligned "key    value" table, sorted by key.
+// Used by `status` and `read` in their default (non-JSON) output.
+func printKV(w io.Writer, m map[string]string) {
+	keys := make([]string, 0, len(m))
+	width := 0
+	for k := range m {
+		keys = append(keys, k)
+		if len(k) > width {
+			width = len(k)
+		}
+	}
+	sort.Strings(keys)
+	for _, k := range keys {
+		fmt.Fprintf(w, "%-*s  %s\n", width, k, m[k])
+	}
+}
+
+// parseKVArgs turns ["key=value", "other=1"] positional args into a map,
+// used by `write` and as auth method params on `login`.
+func parseKVArgs(args []string) (map[string]string, error) {
+	out := map[string]string{}
+	for _, a := range args {
+		k, v, ok := strings.Cut(a, "=")
+		if !ok {
+			return nil, fmt.Errorf("expected key=value, got %q", a)
+		}
+		out[k] = v
+	}
+	return out, nil
+}