fix: anchor the new "Portal Guide" & "Videos" header dropdowns

The nb-quicknav popovers are positioned via explicit CSS anchor-positioning
pairs (anchor-name on the button + position-anchor on the menu) keyed per
popover id. The two new menus (nb-pop-guide, nb-pop-videos) had no such
pairs, so their popovers opened unanchored (wrong position / "broken").
Add the missing anchor-name/position-anchor pairs and bump the CSS
cache-buster to 2.9.42.

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

docs/static/v2_elite.css

@@ -1372,8 +1372,12 @@ input[type="text"] {
 /* Explicit anchor pairing per button↔menu — do NOT rely on the popover's
    implicit anchor (it isn't established reliably, leaving the menu in its
    static position over the button). */
+[popovertarget="nb-pop-guide"]    { anchor-name: --nb-a-guide; }
+#nb-pop-guide    { position-anchor: --nb-a-guide; }
 [popovertarget="nb-pop-digest"]   { anchor-name: --nb-a-digest; }
 #nb-pop-digest   { position-anchor: --nb-a-digest; }
+[popovertarget="nb-pop-videos"]   { anchor-name: --nb-a-videos; }
+#nb-pop-videos   { position-anchor: --nb-a-videos; }
 [popovertarget="nb-pop-k8s"]      { anchor-name: --nb-a-k8s; }
 #nb-pop-k8s      { position-anchor: --nb-a-k8s; }
 [popovertarget="nb-pop-delivery"] { anchor-name: --nb-a-delivery; }

v2-mkdocs.yml

@@ -115,7 +115,7 @@ extra:
 extra_css:
   - https://fonts.googleapis.com/css2?family=Inter:wght@400;500;700&display=swap
   - static/extra.css
-  - static/v2_elite.css?v=2.9.39
+  - static/v2_elite.css?v=2.9.42
 
 extra_javascript:
   - static/v2_filter.js?v=2.9.19