Adapt parser and tests to new sompyler AST slot names

Sompyler commit c3b51bc renamed slots across the board:
- offset.stem_note → line.stem_note (parentSlot 'offset' → 'line')
- motif.stem_note → line.stem_note (parentSlot 'motif' → 'line')
- clause.note/pause/stack → seq.note/pause/stack (parentSlot 'clause' → 'seq')
- stem_note.chain is now a real hierarchical node (depth 04) between
  line.stem_note and chain.clause; clauses are now its children, not
  direct children of stem_note

Also adds:
- offset.motifs[] for line.motif invocations at tick positions
- stem_note.writeToName from stem_note.write_to positional
- adjacent prop already stored; new tests verify True/False/absent

PaneFO.js: show offset motif invocations inline (label + chord)
test-parser.mjs: update synthetic fixtures to new depths/slot names;
  add tests for line.motif, stem_note.write_to, adjacent prop

static/components/PaneFO.js

@@ -193,8 +193,11 @@ export const PaneFO = {
                         fields: [
                             { key: 'tick', value: node.tick, editable: false },
                             { key: 'stem notes', value: node.stemNotes.map(snLabel).join(', ') || '—', editable: false },
+                            node.motifs?.length
+                                ? { key: 'motifs', value: node.motifs.map(m => m.chord ? `${m.label}(${m.chord})` : m.label).join(', '), editable: false }
+                                : null,
                             ...unknownPropFields(node),
-                        ],
+                        ].filter(Boolean),
                         onChange: null,
                     }),
                 );