docs: getting-started guide, settings reference, and README restructure (#23)

Moves 19 version-highlight blocks out of the README into CHANGELOG.md
(where they already existed). The README now opens with install, first
run, recommended starting profile, and a link to the full guide at
docs/getting-started.md. The guide lists every user-facing toggle with
its DataStore key and default value.

The release-drift check no longer requires highlights in the README; it
checks the CHANGELOG instead.

Fixes #23

Author: SysAdminDoc