On Windows, many common commands like `dir`, `copy`, `del`, etc., are internal to `cmd.exe` and do not exist as separate executables on the disk. This updates `scanPathExecutables` to explicitly include these built-ins when running on Windows, ensuring a consistent autocomplete experience for Windows users.
When typing outside of shell mode (e.g., using `@` completion), the `useShellCompletion` hook was continuously re-rendering and executing its `useEffect` because `performCompletion` was recreated on every keystroke (since its `query` dependency changed).
Because `enabled` was false, the effect unconditionally called `setSuggestions([])`, rapidly overriding the suggestions populated by `useAtCompletion` and causing severe UI flickering.
This splits the effect to ensure `setSuggestions([])` is only called once when `enabled` becomes false, stabilizing the suggestions list.
jacob314