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

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

frontend/src/lib/shared/discussion/commentDeepLink.spec.ts

@@ -0,0 +1,14 @@
+import { describe, it, expect } from 'vitest';
+import { buildCommentHref } from './commentDeepLink';
+
+describe('buildCommentHref', () => {
+	it('includes both commentId and annotationId when annotationId is present', () => {
+		const href = buildCommentHref('doc-1', 'comment-2', 'annot-3');
+		expect(href).toBe('/documents/doc-1?commentId=comment-2&annotationId=annot-3');
+	});
+
+	it('omits annotationId when null', () => {
+		const href = buildCommentHref('doc-1', 'comment-2', null);
+		expect(href).toBe('/documents/doc-1?commentId=comment-2');
+	});
+});