* Add Quick Shell plugin for launcher commands
Introduces `/qs` launcher prefix to run shell commands in an interactive
terminal. Features dynamic shell completions (Fish/Bash), command
history, user snippets, and directory navigation.
* Rename quick-shell plugin to shell command plugin
* Update thumbnail.webp
* Document shell dependencies and filter completions by current word
Filter bash compgen completions to the current word being typed. Declare
`sh`, `ls`, `fish`, and `bash` as plugin dependencies.
