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/components/PaneCP.js

@@ -49,7 +49,7 @@ export const PaneCP = {
                 props.store.rawScoreText = raw;
                 const patched = patchScore(raw, props.store.scoreModel.instruments, props.store.scoreModel.bars);
                 await putScoreText(patched, props.store.credentials);
-                props.store.synthesisStatus = { frozen: false, progress: 0 };
+                props.store.synthesisStatus = { frozen: false, currently_rendered_notes: 0, notes_in_total: 0 };
             } catch (e) {
                 exportError.value = e.message;
             } finally {