feat: Implement pinned comments, locked comment threads, and a two-level reply structure with @mentions.

public/s/css/f0ck.css

@@ -4086,4 +4086,53 @@ input#s_avatar {
 .cancel-edit-btn {
   background: #666;
   color: white;
+}
+
+/* Pinned comments */
+.comment.pinned {
+  background: rgba(var(--accent-rgb, 153, 255, 0), 0.1);
+  border-left: 3px solid var(--accent);
+}
+
+.pinned-badge {
+  background: var(--accent);
+  color: var(--black);
+  padding: 2px 6px;
+  border-radius: 3px;
+  font-size: 0.75em;
+  font-weight: bold;
+  margin-right: 8px;
+}
+
+.admin-pin-btn {
+  background: none;
+  border: none;
+  cursor: pointer;
+  font-size: 0.9em;
+  padding: 0 4px;
+  margin-left: 5px;
+  opacity: 0.6;
+  transition: opacity 0.2s;
+}
+
+.admin-pin-btn:hover {
+  opacity: 1;
+}
+
+/* Two-level comment replies */
+.comment-replies {
+  margin-left: 40px;
+  border-left: 2px solid var(--gray);
+  padding-left: 15px;
+  margin-top: 10px;
+}
+
+.comment.reply {
+  background: rgba(0, 0, 0, 0.1);
+}
+
+.reply-mention {
+  color: var(--accent);
+  font-weight: bold;
+  margin-right: 4px;
 }