docs: remove version-switcher + drop external-link arrow on navbar

Two small navbar cleanups:

1. Drop ``version-switcher`` from ``navbar_center`` and remove the
   companion ``switcher``/``json_url``/``version_match`` config. The
   project does not ship versioned docs, so the "Choose version"
   dropdown was a permanent no-op stub.
2. Switch the cross-subsite anchor template from ``nav-external`` to
   ``nav-internal``. The three links (MetaSim / RoboVerse / FAQ)
   point at sibling subsites on the same roboverse.wiki deployment;
   pydata's ↗ arrow icon for external links misled readers.

Author: geng-haoran

docs/source/_templates/navbar-nav.html

@@ -1,12 +1,18 @@
 {# Override pydata_sphinx_theme's navbar-nav: render ONLY ``external_links``,
    not the top-level toctree entries. We use the left sidebar (configured via
-   html_sidebars = {"**": ["globaltoc.html"]}) for in-site navigation, so the
-   top bar is reserved for the two cross-subsite links (MetaSim ↔ RoboVerse). #}
+   html_sidebars = {"**": ["sidebar-section-nav.html"]}) for in-site
+   navigation, so the top bar is reserved for the cross-subsite links
+   (MetaSim / RoboVerse / FAQ).
+
+   Note we tag the anchors as ``nav-internal`` even though the URLs are
+   absolute paths. They're internal to the same roboverse.wiki deployment
+   — pydata's ``nav-external`` class would otherwise append a small "↗"
+   arrow icon that misleads readers into thinking they leave the site. #}
 <nav>
   <ul class="bd-navbar-elements navbar-nav">
     {%- for external_link in theme_external_links %}
     <li class="nav-item">
-      <a class="nav-link nav-external" href="{{ external_link.url }}">
+      <a class="nav-link nav-internal" href="{{ external_link.url }}">
         {{ external_link.name }}
       </a>
     </li>

docs/source/conf.py

@@ -55,8 +55,6 @@
 html_logo = "_static/RoboVerse86.22.svg"
 html_favicon = "_static/logo.png"
 
-json_url = "_static/version_switcher.json"
-version_match = os.environ.get("READTHEDOCS_VERSION")
 html_theme_options = {
     "show_nav_level": 1,
     "use_edit_page_button": True,
@@ -75,20 +73,18 @@
     "logo": {
         "image_dark": "_static/RoboVerse86.22.svg",
     },
-    # Top navbar shows only the two cross-subsite links (MetaSim ↔ RoboVerse)
-    # via ``external_links`` (rendered through our overridden navbar-nav
-    # template). All in-site navigation lives in the left sidebar.
-    "navbar_center": ["version-switcher", "navbar-nav"],
+    # Top navbar shows only the cross-subsite links (MetaSim / RoboVerse /
+    # FAQ) via ``external_links`` (rendered through our overridden
+    # navbar-nav template). All in-site navigation lives in the left
+    # sidebar. ``version-switcher`` is intentionally NOT in
+    # ``navbar_center`` — the project does not ship versioned docs.
+    "navbar_center": ["navbar-nav"],
     "external_links": [
         {"name": "MetaSim", "url": "/metasim/"},
         {"name": "RoboVerse", "url": "/roboverse/"},
         {"name": "FAQ", "url": "/FAQ/"},
     ],
     "show_version_warning_banner": False,
-    "switcher": {
-        "json_url": json_url,
-        "version_match": version_match,
-    },
     "sidebarwidth": "150px",
 }