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/WhoWhenSection.svelte

@@ -16,7 +16,6 @@ let {
 	dateIso = $bindable(''),
 	precision = $bindable<DatePrecision>('DAY'),
 	endDateIso = $bindable(''),
-	rawDate = '',
 	initialDateIso = '',
 	initialLocation = '',
 	initialSenderName = '',
@@ -30,7 +29,6 @@ let {
 	dateIso?: string;
 	precision?: DatePrecision;
 	endDateIso?: string;
-	rawDate?: string;
 	initialDateIso?: string;
 	initialLocation?: string;
 	initialSenderName?: string;
@@ -179,15 +177,6 @@ $effect(() => {
 				{/if}
 			</div>
 			<input type="hidden" name="metaDateEnd" value={showEndDate ? endDateIso : ''} />
-
-			<!-- Originaltext (read-only raw cell): labelled static text, not a disabled input. -->
-			{#if rawDate && rawDate.trim().length > 0}
-				<div data-testid="who-when-raw">
-					<p class="mb-1 block text-sm font-medium text-ink-2">{m.date_original_label()}</p>
-					<p class="font-sans text-sm text-ink">{rawDate}</p>
-					<input type="hidden" name="metaDateRaw" value={rawDate} />
-				</div>
-			{/if}
 		{/if}
 
 		<!-- Absender (required in upload mode — row 1, col 2) -->