fix(page-templates): clean up page-embed node chrome (#39)

Two design problems on the whole-page embed (pageEmbed) node:

- Double selection frame: the generic square cyan .ProseMirror-selectednode
  outline stacked on top of the rounded .includeWrap border. Add node-pageEmbed
  to the existing outline:none rule (already covering the transclusion nodes) so
  only the single rounded border remains.
- Redundant 'open source' controls: the floating toolbar's external-link button
  duplicated the header badge title link. Remove the toolbar button; the badge
  title is now the single way to open the source (kept Refresh + ... menu).
  Also swap the badge fallback icon IconArrowsMaximize (read as 'expand') for a
  neutral IconFileText.

Follow-ups from review: render the badge whenever the source resolves (so the
only open-source link can't vanish when title+icon are empty), and label the
link (title/aria-label) + add the 'Open source page' i18n key (en-US, ru-RU).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/client/src/features/editor/components/transclusion/transclusion.module.css

@@ -183,7 +183,8 @@
 }
 
 :global(.react-renderer.node-transclusionSource.ProseMirror-selectednode),
-:global(.react-renderer.node-transclusionReference.ProseMirror-selectednode) {
+:global(.react-renderer.node-transclusionReference.ProseMirror-selectednode),
+:global(.react-renderer.node-pageEmbed.ProseMirror-selectednode) {
   outline: none;
 }