refactor: move shared utilities to lib/shared/ sub-packages

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/shared/discussion/comment.ts

@@ -0,0 +1,5 @@
+export function extractQuote(content: string): { quote: string | null; body: string } {
+	const match = content.match(/^>\s*"(.+?)"\s*\n\n?([\s\S]*)$/);
+	if (match) return { quote: match[1], body: match[2] };
+	return { quote: null, body: content };
+}