refactor: split editor.rs into editor/ widget modules

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>

src/editor/mod.rs

@@ -0,0 +1,107 @@
+//! egui editor: assembly + control layout.
+//!
+//! The aggregator. Builds the editor window and lays out the heading, the meter panel
+//! ([`meter`]), the rolling plot ([`plot`]), and the (placeholder) per-channel slider columns.
+//! Each visualiser owns its GUI state and drawing in its submodule; this module wires them
+//! together and holds the shared [`EditorState`]. When the UI is redesigned the slider columns
+//! get replaced and the visualisers stay as self-contained widgets.
+
+use nih_plug::prelude::*;
+use nih_plug_egui::{
+    create_egui_editor,
+    egui::{self, Vec2},
+    resizable_window::ResizableWindow,
+    widgets,
+};
+use std::sync::Arc;
+
+use crate::meters::Meters;
+use crate::params::{Codename206Params, CompressorParams};
+use crate::Codename206;
+
+mod meter;
+mod plot;
+
+/// Bottom of the dB scale shared by the meters and the plot (top is 0 dBFS).
+const METER_FLOOR_DB: f32 = -60.0;
+
+/// GUI-side editor state (not persisted): the per-widget state for the meter panel and the plot.
+#[derive(Default)]
+struct EditorState {
+    meter: meter::MeterState,
+    plot: plot::PlotState,
+}
+
+/// Build the plugin editor over shared handles to the params and meter state.
+pub(crate) fn create(params: Arc<Codename206Params>, meters: Arc<Meters>) -> Option<Box<dyn Editor>> {
+    let egui_state = params.editor_state.clone();
+    create_egui_editor(
+        params.editor_state.clone(),
+        EditorState::default(),
+        |_, _| {},
+        move |egui_ctx, setter, state| {
+            // Keep frames coming so the meters animate and the lamp can time out while open.
+            egui_ctx.request_repaint();
+
+            // One column of controls for a single compressor channel (placeholder layout).
+            let band_col = |ui: &mut egui::Ui, title: &str, p: &CompressorParams| {
+                ui.strong(title);
+                ui.label("Pre-gain");
+                ui.add(widgets::ParamSlider::for_param(&p.pre_gain_db, setter));
+                ui.add(widgets::ParamSlider::for_param(&p.detection, setter));
+                ui.label("Threshold");
+                ui.add(widgets::ParamSlider::for_param(&p.threshold_db, setter));
+                ui.label("Ratio");
+                ui.add(widgets::ParamSlider::for_param(&p.ratio, setter));
+                ui.label("Knee");
+                ui.add(widgets::ParamSlider::for_param(&p.knee_db, setter));
+                ui.label("Attack");
+                ui.add(widgets::ParamSlider::for_param(&p.attack_ms, setter));
+                ui.label("Release");
+                ui.add(widgets::ParamSlider::for_param(&p.release_ms, setter));
+                ui.label("Makeup");
+                ui.add(widgets::ParamSlider::for_param(&p.makeup_db, setter));
+                ui.add(widgets::ParamSlider::for_param(&p.bypass, setter));
+            };
+
+            // Resizable window; vertical scroll so every control stays reachable even when the
+            // window is small. (Placeholder layout — the redesign will replace the slider columns.)
+            ResizableWindow::new("editor")
+                .min_size(Vec2::new(480.0, 320.0))
+                .show(egui_ctx, egui_state.as_ref(), |ui| {
+                    egui::ScrollArea::vertical().show(ui, |ui| {
+                        ui.heading(Codename206::NAME);
+                        meter::draw(ui, &meters, &mut state.meter);
+                        ui.separator();
+                        plot::draw(ui, &meters, &mut state.plot);
+                        ui.separator();
+                        // Global controls stacked vertically so they never overflow sideways.
+                        egui::Grid::new("globals").num_columns(2).show(ui, |ui| {
+                            ui.label("Xover Lo/Mid");
+                            ui.add(widgets::ParamSlider::for_param(&params.crossover_low_hz, setter));
+                            ui.end_row();
+                            ui.label("Xover Mid/Hi");
+                            ui.add(widgets::ParamSlider::for_param(&params.crossover_high_hz, setter));
+                            ui.end_row();
+                            ui.label("Look-ahead");
+                            ui.add(widgets::ParamSlider::for_param(&params.look_ahead_ms, setter));
+                            ui.end_row();
+                            ui.label("Ceiling");
+                            ui.add(widgets::ParamSlider::for_param(&params.output_ceiling_db, setter));
+                            ui.end_row();
+                            ui.label("Lim Release");
+                            ui.add(widgets::ParamSlider::for_param(&params.limiter_release_ms, setter));
+                            ui.end_row();
+                        });
+                        ui.separator();
+                        ui.columns(4, |cols| {
+                            band_col(&mut cols[0], "LOW", &params.low);
+                            band_col(&mut cols[1], "MID", &params.mid);
+                            band_col(&mut cols[2], "HIGH", &params.high);
+                            band_col(&mut cols[3], "ALL", &params.all);
+                        });
+                    });
+                });
+        },
+    )
+}