perf(comment): static comment renderer + lazy editors + memoized list (#340)

The comment panel lagged for seconds on open and stuttered on every resolve/apply
with many comments (real case: 30 open + 326 resolved ≈ 356 threads), because each
comment body mounted a full TipTap/ProseMirror editor, both tabs mounted at once,
and any mutation re-rendered the whole list.

- CommentContentView: static recursive renderer of comment ProseMirror JSON (no
  editor instance) for the read-only body — supports exactly CommentEditor's node
  set (doc/paragraph/text/hardBreak/mention) + marks (bold/italic/strike/code/
  link), reproducing the 3-level DOM nesting for pixel-identical CSS. Unknown
  node/mark or unparseable content degrades that one comment to the read-only
  CommentEditor; legacy non-JSON strings render as plain text.
  SECURITY: link hrefs are protocol-allowlisted (safeHref, mirroring
  @tiptap/extension-link) so a stored comment with a `javascript:`/`data:` href
  cannot XSS — the old TipTap read-only path sanitized this; the static renderer
  must too. Control-char smuggling (java\tscript:) is stripped before the check.
- MentionContent extracted from MentionView, shared by the TipTap NodeView and the
  static renderer (identical user/page-mention behavior).
- keepMounted={false} on the tabs: the inactive tab no longer mounts its editors.
- Lazy reply editor: a stub until click/focus, then the real editor (kept mounted
  so the draft survives thread re-renders).
- React.memo(CommentListItem) + a childrenByParent map (replaces the per-thread
  O(n^2) filter) + localized reply-send pending state: resolve/apply/reply now
  re-render only the touched thread.
- Progressive first paint: useCommentsQuery no longer blocks on hasNextPage.

Gate: client comment+mention suites 22/22 passed, tsc --noEmit 0.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/client/src/features/editor/components/mention/mention-view.tsx

@@ -11,9 +11,19 @@ import {
 import { extractPageSlugId } from "@/lib";
 import classes from "./mention.module.css";
 
-export default function MentionView(props: NodeViewProps) {
-  const { node } = props;
-  const { label, entityType, entityId, slugId, anchorId } = node.attrs;
+interface MentionAttrs {
+  label?: string;
+  entityType?: string;
+  entityId?: string;
+  slugId?: string;
+  anchorId?: string;
+}
+
+// Presentational mention renderer (no NodeViewWrapper). Shared by the editor
+// NodeView (MentionView) and the static comment renderer (CommentContentView)
+// so mention click/nav/icon behavior stays identical outside of an editor.
+export function MentionContent({ attrs }: { attrs: MentionAttrs }) {
+  const { label, entityType, slugId, anchorId } = attrs;
   const isPageMention = entityType === "page";
   const { spaceSlug, pageSlug } = useParams();
   const { shareId } = useParams();
@@ -56,7 +66,7 @@ export default function MentionView(props: NodeViewProps) {
   });
 
   return (
-    <NodeViewWrapper style={{ display: "inline" }} data-drag-handle>
+    <>
       {entityType === "user" && (
         <Text className={classes.userMention} component="span">
           @{label}
@@ -139,6 +149,14 @@ export default function MentionView(props: NodeViewProps) {
           </span>
         </Anchor>
       )}
+    </>
+  );
+}
+
+export default function MentionView(props: NodeViewProps) {
+  return (
+    <NodeViewWrapper style={{ display: "inline" }} data-drag-handle>
+      <MentionContent attrs={props.node.attrs} />
     </NodeViewWrapper>
   );
 }