fix(qa): resolve UI bugs from #216 and #218

Public sharing (#218):
- Bind public-share content to the requested shareId. getSharedPage now
  enforces dto.shareId (forwarded from /share/:shareId/p/:slug): the page must
  be reachable THROUGH that exact share (its own share, or an includeSubPages
  ancestor that contains it). A forged/mismatched shareId 404s instead of
  rendering off the slug alone and no longer leaks the real canonical key via
  redirect. A request with no shareId keeps the legacy slug-capability path.
- Trim /shares/page-info: drop internal metadata (creatorId, spaceId,
  workspaceId, contributorIds, lastUpdated*, parent/position, lock/template
  flags, timestamps) from the anonymous payload.
- Default share-to-web includeSubPages to false (opt-in), so enabling a share
  no longer silently exposes the whole sub-tree (#216).

Editor (#218):
- Harden the new-page pre-sync window: the body editor is kept read-only until
  the collab provider is Connected and synced, so early keystrokes can't land
  only in local ProseMirror and then be clobbered by the server's empty doc.
- Surface a "Connecting… (read-only)" affordance during the static phase so
  input isn't silently swallowed.

Other:
- Breadcrumb: resolve from the page's own ancestor data (/pages/breadcrumbs)
  instead of waiting for the lazily-built sidebar tree, so deep pages don't
  render a blank breadcrumb for seconds.
- Pasting GitHub `> [!type]` callouts now converts to a callout node instead of
  a literal blockquote (new marked extension wired into markdownToHtml).

Tests: editor-sync-state gate (client), getSharedPage share-binding (server),
github-callout markdown conversion (editor-ext).

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

apps/client/src/features/page/components/breadcrumbs/breadcrumb.tsx

@@ -16,7 +16,10 @@ import { Link, useParams } from "react-router-dom";
 import classes from "./breadcrumb.module.css";
 import { SpaceTreeNode } from "@/features/page/tree/types.ts";
 import { buildPageUrl } from "@/features/page/page.utils.ts";
-import { usePageQuery } from "@/features/page/queries/page-query.ts";
+import {
+  usePageQuery,
+  usePageBreadcrumbsQuery,
+} from "@/features/page/queries/page-query.ts";
 import { extractPageSlugId } from "@/lib";
 import { useMediaQuery } from "@mantine/hooks";
 import { useTranslation } from "react-i18next";
@@ -38,14 +41,43 @@ export default function Breadcrumb() {
   const { data: currentPage } = usePageQuery({
     pageId: extractPageSlugId(pageSlug),
   });
+  // The page's own ancestor chain, fetched independently of the lazily-built
+  // sidebar tree so a deep page doesn't render a blank breadcrumb for seconds
+  // while the tree backfills (#218).
+  const { data: ancestors } = usePageBreadcrumbsQuery(currentPage?.id);
   const isMobile = useMediaQuery("(max-width: 48em)");
 
   useEffect(() => {
-    if (treeData?.length > 0 && currentPage) {
+    if (!currentPage) return;
+
+    // Prefer the sidebar tree once it actually contains this page's ancestor
+    // chain — it stays live with renames/moves happening in the sidebar.
+    if (treeData?.length > 0) {
       const breadcrumb = findBreadcrumbPath(treeData, currentPage.id);
-      setBreadcrumbNodes(breadcrumb || null);
+      if (breadcrumb) {
+        setBreadcrumbNodes(breadcrumb);
+        return;
+      }
     }
-  }, [currentPage?.id, treeData]);
+
+    // Otherwise fall back to the page's own ancestor data so the breadcrumb
+    // resolves immediately instead of staying blank.
+    if (ancestors?.length) {
+      setBreadcrumbNodes(
+        (ancestors as any[]).map((node) => ({
+          id: node.id,
+          slugId: node.slugId,
+          name: node.title,
+          icon: node.icon,
+          position: node.position,
+          spaceId: node.spaceId,
+          parentPageId: node.parentPageId,
+          hasChildren: node.hasChildren ?? false,
+          children: [],
+        })) as SpaceTreeNode[],
+      );
+    }
+  }, [currentPage?.id, treeData, ancestors]);
 
   const HiddenNodesTooltipContent = () =>
     breadcrumbNodes?.slice(1, -1).map((node) => (