Add MIT LICENSE file (Cargo.toml already declares MIT). Record in
DECISIONS.md that the open-source publish/rename plan is dropped: the
tool is for personal use, distributed as an Arch package via the private
moonarch repo and used primarily as a Waybar widget.
PLAN.md: 5-phase plan to publish as a multi-protocol headset tool
(rename away from Corsair trademark, abstract device layer, port
additional protocols, publish, upstream to HeadsetControl).
DECISIONS.md: rationale for GPLv3 relicense, naming constraints, and
the multi-protocol architecture.