feat(document): stop surfacing the raw cell in the detail drawer

The detail drawer's date cell rendered DocumentDate whenever a date OR a
raw cell was present (`{#if documentDate || metaDateRaw}`). For an
undated, raw-only document that meant the verbatim import text leaked
into the view. Tighten the guard to `{#if documentDate}` so such a
document shows "—". The raw prop is still passed through for the SEASON
word on dated documents. Covered by a new test.

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

frontend/src/lib/document/DocumentMetadataDrawer.svelte

@@ -113,7 +113,7 @@ function getFullName(person: Person): string {
 				<div>
 					<dt class="font-sans text-xs font-medium text-ink-3">{m.doc_details_field_date()}</dt>
 					<dd class="text-ink">
-						{#if documentDate || metaDateRaw}
+						{#if documentDate}
 							<DocumentDate
 								iso={documentDate}
 								precision={metaDatePrecision}