Delete the action.accumulate / action.clear node kinds (superseded by the
typed action.array.* nodes). Old panels are migrated transparently on load
(xml.ts migrateLegacyArrayNode): accumulate→array.push, clear→array.clear,
and legacy single-`array` export folded into the JSON `columns` form.
Export CSV column pickers now use array-local dropdowns instead of free-text
+ datalist, matching the action.array.* node inspectors. Removes the now-dead
flow-array-names datalist and legacy single-`array` fallbacks.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
