DRY up wall and reply rendering with ThreadedReplyList component

Extract shared ThreadedReplyList component and use it in PostDetailPage,
ExternalContentPage, and ProfilePage wall tab. Wall comments now also fetch
sub-replies via useComments so they render with the same threaded/threadedLast
connector-line pairing as replies.

src/components/ThreadedReplyList.tsx

@@ -0,0 +1,31 @@
+import type { NostrEvent } from '@nostrify/nostrify';
+import { NoteCard } from '@/components/NoteCard';
+
+export interface ThreadedReply {
+  reply: NostrEvent;
+  firstSubReply?: NostrEvent;
+}
+
+interface ThreadedReplyListProps {
+  replies: ThreadedReply[];
+}
+
+/**
+ * Renders a flat list of replies where each top-level reply is optionally
+ * followed by its first sub-reply, using NoteCard's threaded/threadedLast
+ * connector-line styling for visual continuity.
+ */
+export function ThreadedReplyList({ replies }: ThreadedReplyListProps) {
+  return (
+    <>
+      {replies.map(({ reply, firstSubReply }) => (
+        <div key={reply.id}>
+          <NoteCard event={reply} threaded={!!firstSubReply} />
+          {firstSubReply && (
+            <NoteCard event={firstSubReply} threadedLast />
+          )}
+        </div>
+      ))}
+    </>
+  );
+}