Document AR=0 indefinite-playback behaviour in the UI

The User Guide says AR=0 means the note continues indefinitely (with
pitch envelope auto-repeating if T bit 7 is clear). The tool caps the
release tail at 2 s for bounded audition; surface that in the Hold
tooltip and AR field hint so users know to enable Hold to hear it.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: kieranhj

index.html

@@ -46,7 +46,7 @@ <h2>Visualisation</h2>
             <div class="transport">
               <button id="play">Play</button>
               <button id="stop">Stop</button>
-              <label class="hold-toggle" title="Hold the note indefinitely (BBC SOUND duration -1)"><input type="checkbox" id="hold" /> Hold</label>
+              <label class="hold-toggle" title="Hold the note indefinitely (BBC SOUND duration -1). Also use this to audition AR=0 envelopes — on a real BBC AR=0 means the note continues indefinitely, but this tool otherwise caps the release tail at 2 s."><input type="checkbox" id="hold" /> Hold</label>
               <button id="share-link" title="Copy a shareable URL with auto-play that reproduces the current envelope and sound">Copy share link</button>
               <button id="run-emulator" title="Open bbc.xania.org with the current ENVELOPE and SOUND auto-running">Run in BBC emulator ↗</button>
             </div>

src/main.ts

@@ -38,7 +38,7 @@ const AMP_FIELDS: FieldSpec[] = [
   { key: "ad",  code: "AD",  label: "Decay rate",          min: -127, max: 127, hint: "amplitude change per centisecond during decay" },
   { key: "ald", code: "ALD", label: "Sustain start level", min: 0,    max: 126, hint: "level at end of decay (start of sustain)" },
   { key: "as",  code: "AS",  label: "Sustain rate",        min: -127, max: 127, hint: "amplitude change per centisecond during sustain (until SOUND duration ends)" },
-  { key: "ar",  code: "AR",  label: "Release rate",        min: -127, max: 127, hint: "amplitude change per centisecond during release; usually negative" },
+  { key: "ar",  code: "AR",  label: "Release rate",        min: -127, max: 127, hint: "amplitude change per centisecond during release; usually negative. AR=0 plays indefinitely on a real BBC — enable Hold to audition that here (otherwise the release tail is capped at 2 s)." },
 ];
 
 const ENV_FIELDS: FieldSpec[] = [...PITCH_FIELDS, ...AMP_FIELDS];