Add motif/stem_note display and offset note hierarchy

- parseAstLog: abort on depth jump >1 or missing slot (depth>0)
- buildStemNote: full clause tree (notes/pauses/stacks), editable fields
- buildClause: replaces buildCluster; filters nested clause.chain silently
- buildMotif: builds from voice.motif; sets isStatic
- buildOffset: uses buildStemNote; drops old clusters/chains arrays
- buildVoice: motifs are now objects, not label strings
- PaneSubObjects: static motifs before offsets; motif/offset→stem_note drill-down
- PaneFO: motif + stem_note FO cases; unknownProps display helper
- PaneCP: motif + stem_note shortView cases
- test-parser.mjs: 21 new synthetic tests for motif/clause/stack/guards

static/components/PaneCP.js

@@ -30,6 +30,10 @@ function shortView(node) {
             return { typeTag: 'voice', label: node.name, meta: [] };
         case 'offset':
             return { typeTag: 'tick', label: String(node.tick ?? '?'), meta: [] };
+        case 'motif':
+            return { typeTag: 'motif', label: node.label, meta: node.isStatic ? [{ key: 'static', value: '✓' }] : [] };
+        case 'stem_note':
+            return { typeTag: 'stem_note', label: String(node.pitch), meta: [] };
         default:
             return { typeTag: node.type, label: node.type, meta: [] };
     }