refactor: treat Applications and File Search as normal extensions (#1012)

I was digging into an issue that the "File Search" extension does
not appear in the extension list under some cases, then I realized
that, in list_extensions(), "File Search" is another extension that
needs to be processed separately, just like the "Applications"
extension.

Both extensions are of type group/extension, which semantically should
behave like a folder, i.e., they contain sub-extensions, but they
do not. In our implementation, they are more like command extensions.

So we treat them as normal extensions in list_extensioins().

docs/content.en/docs/release-notes/_index.md

@@ -21,6 +21,7 @@ Information about release notes of Coco App is provided here.
 ### ✈️ Improvements
 
 - chore: show error msg (not err code) when installing exts via deeplink fails #1007
+- refactor: treat Applications and File Search as normal extensions #1012
 
 ## 0.9.1 (2025-12-05)