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/share/components/share-modal.tsx

@@ -73,7 +73,10 @@ export default function ShareModal({ readOnly }: ShareModalProps) {
       if (value) {
         await createShareMutation.mutateAsync({
           pageId: pageId,
-          includeSubPages: true,
+          // Opt-in: enabling a share must NOT silently expose the whole
+          // sub-tree (#216). Sub-pages are shared only when the user turns on
+          // the dedicated "Include sub-pages" toggle.
+          includeSubPages: false,
           searchIndexing: false,
         });
       } else if (share && share.id) {