Meter each track and the song, and limit the output at -1 dBFS (#359)

A song could clip at the output without anyone noticing: a track and a
sound item at +12 dB each add up to +24 dB. The Song tab now shows how
loud each track and the whole song are, and a fixed limiter behind the
master keeps every sample under -1 dBFS in the editor and in the game.

- Each track head has a stereo meter up its right edge. The head is
  190 px wide instead of 176.
- Out sits in the corner above the heads, with the loudest peak since
  Play in dB. In the tab header it made the row too wide for a 1280 px
  window, and the inspector lost its fields.
- The meters read AnalyserNodes beside the buses, one per side after a
  channel splitter, so a peak panned hard is not halved. They are tapped
  only while the song plays and its tab is shown.
- A clip lamp lights past 0 dBFS and stays through Stop. The next Play
  or a click on the meter puts it out.
- The meter of a track that mute or solo keeps from being heard is grey.
- Music always plays through a bus of its own, with or without a sound
  FX. That bus is what Out measures.
- The limiter is the one from #326 and needs the FX worklet. Until that
  is loaded the master goes straight out.
- It is 5 ms late. latency() counts that in, so the playhead and the
  alignment of a recorded take follow it.
- Unit tests build SoundLibrary without the limiter, as their wiring
  checks follow every node of a voice.
- Out shows "-inf" while nothing was loud. The UI font has no infinity
  sign, which the font test found.

Tests:
- Unit meter-view 8 new, sound-library 112 (2 new), 3 counter-tests
  each red
- e2e 65 (melektaus-atx): ALL PASSED, 55 checks (3 new). Out wrote
  +16.6 dB, behind the limiter the loudest sample was 0.8913
- Gate (melektaus-atx): 272 files, 4209 tests, one red in the font
  test. Fixed after it, then the font and meter tests ran green.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/editor/Editor.ts

@@ -1039,6 +1039,7 @@ export class Editor implements PlayHost {
     if (this.tab === 'curve') this.curveEditor.tick(dt);
     if (this.tab === 'pattern') this.patternEditor.tick();
     if (this.tab === 'song') this.songEditor.tick();
+    else this.songEditor.hideMeters();
     if (this.tab === 'sound') this.soundEditor.tick();
     // Play repaints the machine tab itself (see `PlaySession.tick`); an editor run has no session
     // to do it, and its states move just the same.