Simplify: remove dead code and redundancy across vue app

- Delete ObjectBasic (defined, never imported)
- ObjectShort: remove unused node prop
- exporter: export stressorToString; use in patchBarMeta (removes inline duplicate)
- PaneFO: import stressorToString from exporter; extract H4 style constant,
  shapeSection() helper, instrOnChange() helper; remove apply param from
  makeChangeHandler (was always () => markDirty()); remove unnecessary ?.
  on always-initialized arrays (variations, labelSpecs, subvariations)
- PaneSubObjects: explicit hasChildren on all item kinds; bars at score
  level get hasChildren based on voices; remove stale kind-list fallback
- ast-parser coerce(): remove unreachable s.trim() check ('' handled above)
- PaneCP: fix post-export synthesisStatus reset to use real field names

static/exporter.js

@@ -171,10 +171,15 @@ function patchInstrumentHeader(text, instruments) {
     return result.join('\n');
 }
 
+export function stressorToString(s) {
+    if (!s?.groups?.length) return '';
+    return s.groups.map(g => g.join(',')).join(';');
+}
+
 function patchBarMeta(doc, bar) {
     const props = [];
-    if (bar.stressor?.groups?.length)
-        props.push(`  stress_pattern: ${bar.stressor.groups.map(g => g.join(',')).join(';')}`);
+    const sp = stressorToString(bar.stressor);
+    if (sp) props.push(`  stress_pattern: ${sp}`);
     if (bar.tempoLevels != null)
         props.push(`  beats_per_minute: ${bar.tempoLevels}`);
     const ub = serializeShape(bar.upperStressBound);