instrument: narrow the live-param publish lock to its own mutex, off the reload's decode

Knob-drag publishes no longer block behind a full reload's WAV decode — a dedicated livePublishMutex_ replaces reloadMutex_ for the seqlock's single-writer contract. Also fixes an editor comment overclaim and two doc restatements.

src/core/instrument/CLAUDE.md

@@ -161,13 +161,8 @@ must live compute, latching the parameters at note on is not acceptable. long te
 automatable parameters."* It rejects the precedent, not one instance of it.
 
 - **Which controls are live is ONE decision, recorded in ONE place** — `isLiveDeckParam` and
-  `liveCommitFor` (`ui/deck_groups`), whose header is the home for why each excluded control is
-  excluded. Continuous playback controls go live: the six filter tone/modulation knobs, and
-  every stage time and stage level on all three envelopes. Everything else reloads or drops to
-  the voice-param rebuild. **FIVE continuous controls are outside the live set** — pitch
-  key-track, velocity→cutoff depth, and Trigger's %-length, fade-in and fade-out — so a
-  Trigger-mode instance gets no live delivery on its amplitude controls at all; only the filter
-  and pitch-envelope knobs move a sounding one-shot.
+  `liveCommitFor` (`ui/deck_groups`), whose header is THE home for which controls are live and
+  why each exclusion is excluded — see there rather than restating the list here.
 - **Ownership sits ABOVE every snapshot.** `SampleData::live` is a NON-OWNING pointer to the one
   block the shell owns per instance. The member-ordering constraint that enforces it, and why,
   are recorded at `liveParams_` in `shell/instrument/reasampler_processor.h`. A drain voice