Adds a command-line client in cli/ as its own Cargo workspace, depending
on the outline library via a path dependency. Covers exactly the requested
scope: login (stores the API key in the system keyring via the Secret
Service D-Bus protocol, verified against auth.info() before storing),
search (full-text), and get (fetch a document, render its markdown to a
self-contained HTML page, open it in the default browser).
Verified end-to-end against a real Outline instance and the local
gnome-keyring: login stores and search/get retrieve the token purely from
the keyring and saved config, with no environment variables set.
