feat: label code fences so Vicinae can colour them (#10)

src/lib/markdown.ts

@@ -1,3 +1,4 @@
+import { labelCodeFences } from "./code";
 import type { ChatTurn, ThreadMessage } from "./types";
 
 /**
@@ -53,7 +54,13 @@ function renderMessage(message: ThreadMessage, options: TranscriptOptions): stri
   // While a tool is running there is no answer text yet, so the activity line
   // stands in and the user can see what Lam is actually doing.
   const placeholder = message.status ? `_${message.status}…_` : "_Thinking…_";
-  const body = message.text.trim() || (message.isStreaming ? placeholder : "_No response._");
+  const body = message.text.trim()
+    ? // Fences without a language render as a plain dark panel; labelling them
+      // lets Vicinae colour the code (`MdCodeBlock.qml` + KSyntaxHighlighting).
+      labelCodeFences(message.text.trim())
+    : message.isStreaming
+      ? placeholder
+      : "_No response._";
   const sections = [message.isStreaming ? `${body} ${STREAMING_CURSOR}` : body];
 
   // The one thing allowed to break the plain-text rule, because it means