Fix navbar More dropdown and desktop sidebar toctree hierarchy

- Bump header_links_before_dropdown from 8 to 9 so all nav items
  display without overflow into a More dropdown
- Remove shared docs (using-executorch-cpp, building-from-source,
  raspberry_pi_llama_tutorial) from desktop-section toctree so
  Sphinx assigns them to their primary section, fixing missing
  left sidebar on those pages
- Desktop section now owns only the three platform guides

Author: tuzitnik

docs/source/conf.py

@@ -230,7 +230,7 @@
     ],
     "show_version_warning_banner": True,
     "use_edit_page_button": True,
-    "header_links_before_dropdown": 8,
+    "header_links_before_dropdown": 9,
     "navbar_align": "left",
     "navbar_start": ["navbar-logo", "version-switcher"],
     "navbar_center": ["navbar-nav"],

docs/source/desktop-section.md

@@ -62,7 +62,4 @@ Regardless of the target desktop platform, integrating ExecuTorch into a native
 desktop-macos
 desktop-linux
 desktop-windows
-using-executorch-cpp
-using-executorch-building-from-source
-raspberry_pi_llama_tutorial
 ```