feat(document): drop the read-only Originaltext field from the edit form

The "Originaltext:" line in WhoWhenSection rendered the verbatim import
cell (metaDateRaw) as static text plus a hidden input that re-submitted
it on every save. Editors mistook it for an editable field. Remove the
visible line, the hidden round-trip input, and the now-unused rawDate
prop (here and at the DocumentEditLayout call site). The backend's
partial update preserves the stored value, so no data is lost.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/lib/document/DocumentEditLayout.svelte

@@ -209,7 +209,6 @@ async function handleReplaceFile(e: Event) {
 					bind:dateIso={dateIso}
 					bind:precision={datePrecision}
 					bind:endDateIso={dateEndIso}
-					rawDate={doc.metaDateRaw ?? ''}
 					initialDateIso={doc.documentDate ?? ''}
 					initialLocation={doc.location ?? ''}
 					initialSenderName={doc.sender?.displayName ?? ''}