fix: show Add Candidate button in comparison view

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/client/routes/threads/$threadId.tsx

@@ -129,7 +129,7 @@ function ThreadDetailPage() {
 
 			{/* Toolbar: Add candidate + view toggle */}
 			<div className="mb-6 flex items-center gap-3 flex-wrap">
-				{isActive && candidateViewMode !== "compare" && (
+				{isActive && (
 					<button
 						type="button"
 						onClick={openCandidateAddPanel}