fix(editor): guard unresolved page mentions and bare anchor links

A page mention without a slug rendered as a link ending in -null; it now
renders as plain text. A link whose href is a bare #fragment scrolls to
the target on the current page instead of opening about:blank.

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

@@ -224,6 +224,16 @@ export default function LinkView(props: MarkViewProps) {
   const handleNavigate = useCallback(() => {
     if (!href) return;
 
+    if (href.startsWith("#")) {
+      const anchor = href.slice(1);
+      const element =
+        document.querySelector(`[id="${anchor}"]`) ||
+        document.querySelector(`[data-id="${anchor}"]`);
+      element?.scrollIntoView({ behavior: "smooth", block: "start" });
+      navigate(`${location.pathname}#${anchor}`, { replace: true });
+      return;
+    }
+
     if (isInternal) {
       let targetPath = href;
       let anchor = "";