feat(frontend): add accessible DocumentDate render component

Wraps formatDocumentDate with the accessible presentation layer: a non-color
UNKNOWN cue (decorative calendar-with-question icon, aria-hidden, since the
visible "Datum unbekannt" text is the textual cue — WCAG 1.4.1), and the
verbatim meta_date_raw shown as a VISIBLE secondary "Originaltext: …" line for
UNKNOWN/SEASON/APPROX (WCAG 1.4.13, not tooltip-only). raw is rendered via
Svelte default escaping, never {@html} (CWE-79); a component test asserts an
angle-bracket raw value stays inert. Browser test is CI-only.

Refs #666

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/lib/document/DocumentDate.svelte

@@ -0,0 +1,60 @@
+<script lang="ts">
+import { formatDocumentDate, type DatePrecision } from '$lib/shared/utils/documentDate';
+import { getLocale } from '$lib/paraglide/runtime.js';
+import { m } from '$lib/paraglide/messages.js';
+
+type Props = {
+	iso?: string | null;
+	precision?: DatePrecision | null;
+	end?: string | null;
+	raw?: string | null;
+	/** Show the verbatim "Originaltext: …" secondary line when raw is present. */
+	showRaw?: boolean;
+};
+
+let { iso = null, precision = null, end = null, raw = null, showRaw = true }: Props = $props();
+
+const effectivePrecision = $derived<DatePrecision>(precision ?? (iso ? 'DAY' : 'UNKNOWN'));
+const label = $derived(formatDocumentDate(iso, effectivePrecision, end, raw, getLocale()));
+const isUnknown = $derived(effectivePrecision === 'UNKNOWN' || !iso);
+// Only show the verbatim raw line where it adds information the label can't: the
+// season word's source, or the original cell behind an "unknown"/approx date.
+const showRawLine = $derived(
+	showRaw &&
+		!!raw &&
+		raw.trim().length > 0 &&
+		(isUnknown || effectivePrecision === 'SEASON' || effectivePrecision === 'APPROX')
+);
+</script>
+
+<span class="inline-flex flex-col">
+	<span class="inline-flex items-center gap-1">
+		{#if isUnknown}
+			<!-- Non-color cue (WCAG 1.4.1): a calendar-with-question glyph. The visible
+			     "Datum unbekannt" text is the redundant textual cue, so the icon is
+			     decorative and hidden from assistive tech (per Leonie's a11y note). -->
+			<svg
+				class="h-3.5 w-3.5 shrink-0 text-ink-3"
+				viewBox="0 0 24 24"
+				fill="none"
+				stroke="currentColor"
+				stroke-width="2"
+				stroke-linecap="round"
+				stroke-linejoin="round"
+				aria-hidden="true"
+			>
+				<rect x="3" y="4" width="18" height="18" rx="2" />
+				<path d="M3 10h18" />
+				<path d="M9 16a1.5 1.5 0 0 1 3 0c0 1-1.5 1.2-1.5 2.2" />
+				<path d="M10.5 21h.01" />
+			</svg>
+		{/if}
+		<span>{label}</span>
+	</span>
+	{#if showRawLine}
+		<!-- Visible secondary line (WCAG 1.4.13 — not tooltip-only). raw is untrusted
+		     verbatim spreadsheet text; rendered via default Svelte interpolation, which
+		     HTML-escapes it (never {@html}; CWE-79). -->
+		<span class="font-sans text-xs text-ink-2">{m.date_original_label()} {raw}</span>
+	{/if}
+</span>

frontend/src/lib/document/DocumentDate.svelte.test.ts

@@ -0,0 +1,35 @@
+import { describe, it, expect, afterEach } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import { page } from 'vitest/browser';
+import DocumentDate from './DocumentDate.svelte';
+
+// Browser-project (Playwright) tests — CI only.
+
+afterEach(cleanup);
+
+describe('DocumentDate', () => {
+	it('renders a DAY date as a full long date', async () => {
+		render(DocumentDate, { props: { iso: '1943-12-24', precision: 'DAY' } });
+		await expect.element(page.getByText('24. Dezember 1943')).toBeInTheDocument();
+	});
+
+	it('renders MONTH precision as month + year, never a day', async () => {
+		render(DocumentDate, { props: { iso: '1916-06-01', precision: 'MONTH', raw: 'Juni 1916' } });
+		await expect.element(page.getByText('Juni 1916')).toBeInTheDocument();
+	});
+
+	it('shows the verbatim raw cell as a visible secondary line for UNKNOWN (not tooltip-only)', async () => {
+		render(DocumentDate, { props: { iso: null, precision: 'UNKNOWN', raw: 'Sommer?' } });
+		// Real, visible text — not hidden behind a title attribute.
+		await expect.element(page.getByText('Datum unbekannt')).toBeInTheDocument();
+		await expect.element(page.getByText(/Sommer\?/)).toBeVisible();
+	});
+
+	it('renders a malicious raw value as inert escaped text (no element injected)', async () => {
+		const malicious = '<img src=x onerror="alert(1)">';
+		render(DocumentDate, { props: { iso: null, precision: 'UNKNOWN', raw: malicious } });
+		// The payload appears as literal text, and no <img> is created in the DOM.
+		await expect.element(page.getByText(/<img/)).toBeInTheDocument();
+		expect(document.querySelector('img')).toBeNull();
+	});
+});