Add pure template-resolution logic (kctl.ResolveTemplate) with unit tests

internal/kctl/template.go

@@ -0,0 +1,16 @@
+package kctl
+
+import "strings"
+
+// ResolveTemplate replaces "{key}" placeholders in template with the
+// corresponding value from values. Placeholders with no matching key are
+// left untouched, so a misconfigured template is visible (e.g. a literal
+// "{typo}" in the result) instead of silently collapsing to an empty
+// string.
+func ResolveTemplate(template string, values map[string]string) string {
+	result := template
+	for k, v := range values {
+		result = strings.ReplaceAll(result, "{"+k+"}", v)
+	}
+	return result
+}