Move the egui editor from a single editor.rs into an editor/ module: mod.rs
(aggregator: create(), EditorState, layout, placeholder slider columns),
meter.rs (|L|GR|R| meters + ceiling lamp, owns MeterState), and plot.rs
(rolling in/out/GR plot, owns PlotState + PlotHistory). Each visualiser owns
its GUI state; the aggregator composes them. No behavior change.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Mikkeli Matlock