Add peak/RMS detection switch; sweep docs to match code

- Compressor: switchable peak / RMS detection (EnumParam<DetectionMode> in lib.rs
  -> use_rms bool in CompressorSettings; DSP stays framework-agnostic). RMS is a
  one-pole running mean of the linked squared level with a hardcoded 5 ms window,
  updated whenever active so peak<->RMS switching is seamless. New unit test
  (RMS compresses a sine less than peak); 6 tests total.
- README: reconciled Implementation Order checklists with actual progress
  (Stages 1-2 done; look-ahead/latency + basic UI pulled forward), annotated the
  project structure (implemented vs planned), and corrected the Latency and
  Denormal-flushing notes to match the code (set_latency_samples once / constant
  latency; in-code denormal flush). Overview and goals left unchanged.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/lib.rs

@@ -5,6 +5,17 @@ use std::sync::Arc;
 mod dsp;
 use dsp::compressor::{Compressor, CompressorSettings, MAX_LOOKAHEAD_MS};
 
+/// Level-detection mode for the compressor's detector.
+#[derive(Enum, PartialEq, Clone, Copy)]
+enum DetectionMode {
+    #[id = "peak"]
+    #[name = "Peak"]
+    Peak,
+    #[id = "rms"]
+    #[name = "RMS"]
+    Rms,
+}
+
 /// Codename 206 — Stage 2: a single full-band compressor with look-ahead.
 ///
 /// The `CompressorParams` struct is `#[nested]` so the exact same controls + DSP can be
@@ -33,6 +44,8 @@ struct Codename206Params {
 
 #[derive(Params)]
 struct CompressorParams {
+    #[id = "detect"]
+    pub detection: EnumParam<DetectionMode>,
     #[id = "thresh"]
     pub threshold_db: FloatParam,
     #[id = "ratio"]
@@ -80,6 +93,8 @@ impl Default for Codename206Params {
 impl Default for CompressorParams {
     fn default() -> Self {
         Self {
+            detection: EnumParam::new("Detection", DetectionMode::Peak),
+
             threshold_db: FloatParam::new(
                 "Threshold",
                 -18.0,
@@ -188,6 +203,9 @@ impl Plugin for Codename206 {
                     ui.heading(Self::NAME);
                     ui.separator();
                     egui::Grid::new("params").num_columns(2).show(ui, |ui| {
+                        ui.label("Detection");
+                        ui.add(widgets::ParamSlider::for_param(&params.comp.detection, setter));
+                        ui.end_row();
                         ui.label("Threshold");
                         ui.add(widgets::ParamSlider::for_param(&params.comp.threshold_db, setter));
                         ui.end_row();
@@ -260,6 +278,7 @@ impl Plugin for Codename206 {
             release_coef: Compressor::time_to_coef(c.release_ms.value(), self.sample_rate),
             makeup_db: 0.0,
             lookahead_samples: lookahead,
+            use_rms: c.detection.value() == DetectionMode::Rms,
             bypass: c.bypass.value(),
         };