added extensive markdown rendering tests and Kotlin/JS externals for marked library

site/src/jsMain/kotlin/externals/Marked.kt

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+@file:JsModule("marked")
+@file:JsNonModule
+@file:Suppress("UnsafeCastFromDynamic")
+
+package externals
+
+// Kotlin/JS externals for the ESM `marked` package (v12+)
+// Usage in Kotlin: `marked.parse(src)`
+// JS equivalent: `import { marked } from 'marked'; marked.parse(src)`
+external object marked {
+    fun parse(src: String): String
+}