AppShell already wraps each component in div.se-pane; the inner se-pane
had display:none without .active, hiding all content.
Also drop stale movement/part/line/measure bar fields (bar IDs are opaque).
Per RFC §3.2.1.3, VOLUMES, TIMBRE and FM are variation properties. The
previous exporter incorrectly appended them to the first ATTR variation;
they now go into a synthetic root variation (no ATTR) as required.
variationLines() handles these fields directly.
Fix test-parser.mjs fixture paths for standalone execution from repo root.
