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.
Also updated fixtures/ast.log.
Understand the addenda file in connection with
vue3js-app-proposal-for-sdk-claude/README.md and CLAUDE's findings in
response.