feat(cli): add config settings registry

internal/cli/config_registry.go

@@ -0,0 +1,38 @@
+package cli
+
+import (
+	"fmt"
+	"sort"
+	"strconv"
+)
+
+// settingDef describes a configurable global setting for `config list`/`set`.
+type settingDef struct {
+	desc     string
+	validate func(string) error
+}
+
+// settingsRegistry is the authoritative set of valid config keys. `config set`
+// rejects keys absent here; `config list` enumerates them.
+var settingsRegistry = map[string]settingDef{
+	"audit_retention_days": {
+		desc: "Days to keep audit-log entries (integer >= 0)",
+		validate: func(v string) error {
+			n, err := strconv.Atoi(v)
+			if err != nil || n < 0 {
+				return fmt.Errorf("must be an integer >= 0, got %q", v)
+			}
+			return nil
+		},
+	},
+}
+
+// settingKeys returns the registry keys in stable sorted order.
+func settingKeys() []string {
+	ks := make([]string, 0, len(settingsRegistry))
+	for k := range settingsRegistry {
+		ks = append(ks, k)
+	}
+	sort.Strings(ks)
+	return ks
+}