perf: skip redundant re-parse in Markdown.svelte

Author: Algorithm5838

src/lib/components/chat/Messages/Markdown.svelte

@@ -29,9 +29,13 @@
 
 	let tokens = [];
 	let pendingUpdate = null;
+	let lastParsedContent = '';
 
 	const parseTokens = () => {
-		tokens = marked.lexer(replaceTokens(processResponseContent(content), model?.name, $user?.name));
+		const processed = replaceTokens(processResponseContent(content), model?.name, $user?.name);
+		if (processed === lastParsedContent) return;
+		lastParsedContent = processed;
+		tokens = marked.lexer(processed);
 	};
 
 	// Throttle parsing to once per animation frame while streaming