Show Tremolo, Vibrato, Phaser and Flanger as devices that swing (#398)

The four effects that swing were still drawn as rows of numbers. Like
the Delay, the Saturation and the Limiter, each node now shows a device
of a fixed size. Its screen draws what it does over the first seconds
of a sound, and a light plays that in real time, over and over.

- One device for all four (ModulationPanel, ModulationFace and
  modulationView), as KnobPanel is for Gain, Pitch, Mix and Pan. A short
  description gives each its title, plate, buttons and knobs.
- Tremolo, 640x280 in cream: a wave its volume shapes, the volume as
  its outline. It says DOWN TO 50%, EVERY 200 ms and DIPS -6 dB.
- Vibrato, 640x280 in plum: the pitch in semitones, cool below and warm
  above. Under a wet below 1 the dry pitch stands beside it. It says
  how late the voice is (LATE 0.93 ms).
- Phaser, 760x280 in mustard, and Flanger, 680x280 in steel blue: the
  response from 20 Hz to 20 kHz, and under it a lane of the turn or the
  delay over time. The response is drawn where the light is, so the
  notches swirl and the comb jets. A comb finer than a column fills it.
- The light loops over 1, 2, 4 or 8 s, two LFO swings at least, for a
  Flanger as long as its sweep takes to reach 20 ms. The face only
  keeps the editor drawing while something swings and is heard.
- A Rate lamp beside each name goes from dark to lit with the swing.
- Nothing is listened to. The pictures use the worklets' own numbers:
  lfoAt, vibratoSpeedUp (now exported from lfo.ts), the allpass chain
  with its feedback, and the comb, reckoned at 48 kHz.
- Phaser and Flanger take 4 preset columns. Phased Pad was looked at
  in a picture, nothing overlaps.
- Exported from nodes.ts: LFO_SHAPE, lfoShapeOf, TREMOLO_ROWS,
  VIBRATO_ROWS, PHASER_STAGE_ROW and phaserStagesOf. FLANGER_MAX_MS is
  exported from phaser.ts.

Decided here, as the request left the look open:

- A notch counts where the response falls below -3 dB, not some dB
  under the loudest point. Feedback rings peaks far above 0 dB, and the
  first rule counted 7 notches on a Phaser of 12 stages.
- Rate and Depth of Tremolo and Vibrato are big knobs, Wet is small.

Tests:
  Unit modulation-view (stein2): 22 tests, new. Phaser and Flanger
    give the dB of their worklets on a sine within 0.005 dB, the
    Tremolo its samples, the Vibrato the pitch it reads at.
  Counter-check: with the sign of the Phaser's feedback flipped in one
    place, exactly the worklet test fails.
  e2e 34 (atx): ALL PASSED, 142 checks, 4 new. Each device has its
    size, its ports outside, a light that runs by itself, and a button
    and a knob as one undo step each. Picking 8 stages on the Phaser
    draws 4 notches.
  Gate (atx): CHECK EXIT 0, 291 files, 4467 tests.

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

README.md

@@ -47,7 +47,7 @@ npm run build        # writes dist/ and regenerates index.html; the folder is wh
 The browser suite and the three example games need a machine with a GPU:
 
 ```bash
-node tools/seed-e2e.mjs && node tools/e2e.mjs      # the editor, 1970 checks (GM_STEPS=20 for one step)
+node tools/seed-e2e.mjs && node tools/e2e.mjs      # the editor, 1974 checks (GM_STEPS=20 for one step)
                                                    #   every tool signs in first – see the Accounts page
 node tools/seed-jumprun.mjs && node tools/smoke-jumprun.mjs
 node tools/seed-tetris.mjs && node tools/smoke-tetris.mjs