feat(studio): make the FX rack speak the author's language

[vanceingalls]

Wires the plain-language layer that landed in core into the FX rack, to three
UX decisions recorded in plans/audio-fx-ux/README.md §Decided.

What the rack says now

The plain name replaces the DSP name; the DSP name moves inside. A module
reads "Remove Rumble" with "Cutting everything below 80 Hz" under it, and
opening it shows "Details — High-pass" above the knobs. Every knob is renamed
too — plainDef writes the copy over the registry's labels and hints while
leaving range, step, unit and automatability alone, because those are facts and
only the words were ever the problem. A preset's own job name still wins where
it has one: it is the most specific truth available.

Presets read as the complaint they answer. "My voice sounds boomy", with
Boom Tame underneath in small type — which is also how the name gets learned.
The four shelves stay: eighteen sentences in a column is a wall, and
Voice/Fix/Character/Space is already the author's grouping rather than the
registry's. The effect list is untouched and stays in signal order.

da5403026 fixes what that first pass broke: the rack was renamed and the
add menu was not, so an author picked "High-pass" and a module called "Remove
Rumble" appeared — the exact confusion this layer exists to remove,
reintroduced one gesture upstream of it.

Hover-audition

Hovering a preset or an offered effect plays it through the same preview channel
a slider drag already uses, so it costs no new machinery and never touches the
document. Four things have to hold, and each has a test that fails without
it:

1. Leaving puts the stored chain back — captured when the audition starts,
   because the preview channel does not persist and the prop never changes.
2. Applying does not put it back. The audition was the preset, and
   reverting over the write that just landed is a race the author hears as it
   arriving and then leaving again.
3. The panel going away mid-audition reverts — but the teardown must have
   empty deps.
4. Moving between two entries in a shelf is not leaving it.

3 and 4 were bugs in the first commit here, both found by review rather than
by tests, and 8639f3076 fixes them. The teardown was keyed on
onChainPreview, an inline arrow from a component that re-renders on every
playhead tick — so the audition reverted itself about thirty times a second,
during playback, which is the only time there is anything to audition. And
sliding from "Even Out Levels" to the effect beside it kept a measurement
running that then landed on top of the audition next to it. Both are the kind a
static mount cannot see.

Even Out Levels auditions by measuring first — it decodes the track and
analyses it before there is anything to play, so it says "measuring…" while it
works, caches the decode per src, and a run counter drops any result that
arrives after the pointer has left. Reverting puts back both the chain and
the automation, because levelling is a node AND the lane that drives it.

Tone deliberately does not audition: its bands arrive at 0 dB, so there is
nothing to hear, and a hover that changes nothing teaches that hovering does
nothing.

Tests

studio 3685 + 18 todo. Tests that addressed rows by their registry labels now
look them up through EFFECT_COPY, and preset buttons by preset id — those
tests are about which row carries the automate button, not about how it reads,
and hard-coding the words would make every copy edit a test edit.

🤖 Generated with Claude Code

[vanceingalls]

Superseded — replaced by a slice on the new chain to keep the stack linear after the split.