Both panels had a ~90-line near-byte-identical per-item field editor
(boolean->checkbox, number->number, /color/->color, long->textarea, else
text, fields derived from Object.keys(items[0])). Moved into a new
ArrayItemFieldsEditor component in ArrayItemFields.tsx used by both.
SectionTypePanel keeps its own FeaturesGrid special-case (key === 'features'
-> FeaturesEditor) and its empty-array guard ahead of the shared call.
Behavior-preserving (task E4.2).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
