feat(ballast): add Ballast switch-up leveller

Ballast gives every part of a bassline one gain that brings it to the target
loudness, with no compression inside a part. Parts start at note starts,
detected from the audio or taken from MIDI, or on the host's beat grid, so a
patch change on the same note counts too.

- Loudness is K-weighted over each part's first 100 ms, in 10 ms blocks with
  a relative gate, and every part is weighted from rest so the last part does
  not ring into it.
- The audio path is delayed by the tracker's lookahead, the window and a
  5 ms glide, so each gain is in place on its part's first sample.
- Learn takes the next part's loudness as the target. Amount, Range, Measure
  from (leave the sub out), Gate, Output, Bypass.
- Editor shows the last 32 parts in and out, the target, and the spread of
  the last 16 parts.
- Registered in the catalog, workflows, editor-check, README, chain and
  development docs, and the website copy.

website/src/data/plugins.ts

@@ -214,6 +214,21 @@ const COPY: Record<string, Copy> = {
     latency: '< 1 ms',
     tracksNotes: false,
   },
+  ballast: {
+    role: 'Switch-up leveller',
+    metal: 'Ballast is the weight that keeps a ship level.',
+    problem:
+      'Patches at the same peak level still sound louder or quieter, so every switch-up lands at a different loudness and gets hand-set gain or clipping. A compressor evens them out but changes their punch.',
+    points: [
+      'One gain per part: nothing moves inside a note or switch-up.',
+      'Parts start at note starts, from the audio or MIDI, or on the host’s beat grid.',
+      'Loudness is K-weighted (BS.1770) over each part’s first 100 ms; Learn takes a reference part.',
+      'Measure from leaves the sub out of the measurement when Anvil makes it.',
+    ],
+    loadOn: 'Bass, after the sound design',
+    latency: '≈ 172 ms',
+    tracksNotes: true,
+  },
 };
 
 export interface Plugin extends Copy {