fix(document): render full date for precision-less document chips

A TimelineEvent's DocumentRef carries documentDate but no precision, so
formatDocumentOption hit formatDocumentDate's undefined-precision path and
surfaced the UNKNOWN label instead of the date. Default a missing precision
to DAY so the chip shows the full date; add formatDocumentOption unit specs.

Addresses PR #832 review (#781).

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

frontend/src/lib/document/documentTypeahead.spec.ts

@@ -0,0 +1,20 @@
+import { describe, expect, it } from 'vitest';
+import { formatDocumentOption, type DocumentOption } from './documentTypeahead';
+
+describe('formatDocumentOption', () => {
+	it('returns the bare title when no documentDate is present', () => {
+		const doc: DocumentOption = { id: 'd1', title: 'Brief ohne Datum' };
+		expect(formatDocumentOption(doc)).toBe('Brief ohne Datum');
+	});
+
+	// #781: a TimelineEvent's DocumentRef carries documentDate but no precision.
+	// Missing precision must degrade to the full date (DAY), never the UNKNOWN label.
+	it('renders the full date when precision is absent (DocumentRef chip)', () => {
+		const doc: DocumentOption = { id: 'd1', title: 'Umzugsbrief', documentDate: '1925-04-01' };
+		const label = formatDocumentOption(doc);
+		expect(label.startsWith('Umzugsbrief · ')).toBe(true);
+		expect(label).toContain('1925');
+		// The undefined-precision fallback would otherwise surface the UNKNOWN word.
+		expect(label.toLowerCase()).not.toContain('unbekannt');
+	});
+});

frontend/src/lib/document/documentTypeahead.ts

@@ -42,9 +42,12 @@ export function createDocumentTypeahead() {
 
 export function formatDocumentOption(doc: DocumentOption): string {
 	if (!doc.documentDate) return doc.title;
+	// A DocumentRef (#781 timeline chips) carries documentDate but no precision —
+	// default to DAY so the full date renders, rather than the UNKNOWN fallback
+	// formatDocumentDate would otherwise hit for an undefined precision.
 	const label = formatDocumentDate(
 		doc.documentDate,
-		doc.metaDatePrecision as DatePrecision,
+		(doc.metaDatePrecision as DatePrecision) ?? 'DAY',
 		doc.metaDateEnd,
 		null,
 		getLocale()