Replace docs command menu with Command Menu V2 from ui-patterns/CommandMenu.
This introduces the prepackaged folder for the shared Command Menu, which contains commands that are shared across the sites (for example, docs search, theme switcher).
Commands that are only applicable to a single site are now defined within that site's own app folder (put them wherever makes sense for your app folder organization, as long as you use the hooks within a global CommandProvider it will work...)
Tested navigating around, using search and AI on laptop and mobile.
Add all the outstanding pieces for state management of new command menu:
- Pages state (handles routing between command menu views, e.g., docs
search, AI, etc.)
- View state (handles opening and closing and initiation (needed for
lazy loading))
- Query state (handles active search term)
Introduces the first (very small) slice of the new command menu as a `ui-pattern`.
This slice just handles state for available commands. It isn't hooked up to anything yet.
