fix(chat): refine markdown typography

ai_knowledge_base_v2/apps/user-client/src/components/ChatMessage.vue

@@ -23,9 +23,17 @@ const reasoning = computed(() => props.reasoning || parsed.value.reasoning);
 const hasAnswer = computed(() => answer.value.trim().length > 0);
 const renderedContent = computed(() => {
   if (props.role !== "assistant") return answer.value;
-  return hasAnswer.value ? markdown.render(answer.value) : "";
+  return hasAnswer.value ? markdown.render(normalizeStandaloneHeadings(answer.value)) : "";
 });
 
+function normalizeStandaloneHeadings(content: string) {
+  return content.replace(/^([ \t]*)\*\*(.+)\*\*[ \t]*$/gm, (line, indent: string, title: string) => {
+    const normalizedTitle = title.trim();
+    if (!normalizedTitle || normalizedTitle.length > 48 || normalizedTitle.includes("**")) return line;
+    return `${indent}### ${normalizedTitle}`;
+  });
+}
+
 function splitReasoning(content: string) {
   const lower = content.toLowerCase();
   let answer = "";