Extract DocumentEditLayout shared component for the PDF+form split-panel
UI, replacing the old scrolling layout on /documents/[id]/edit with the
same fixed-panel structure used by /enrich/[id]. Removes TranscriptionSection
and FileSectionEdit from the edit page; file upload/replace is now handled
by the shared layout. Delete SaveBar and FileSectionEdit as dead code.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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