fix(dates): make DAY precision locale-aware in formatDocumentDate

DAY precision routed through formatDate() which hard-coded de-DE, so an
en/es reader saw the German month name ("24. Dezember 1943"). Route DAY
through Intl.DateTimeFormat(locale, …) like the other branches, keeping
the T12:00:00 UTC-safety convention. Add en/es DAY+MONTH parity cases to
docs/date-label-fixtures.json (TS-only; the Java title formatter stays
German by design) and assert them in the spec.

Refs #666

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

frontend/src/lib/shared/utils/documentDate.ts

@@ -1,4 +1,4 @@
-import { formatDate, formatMCDate } from './date';
+import { formatMCDate } from './date';
 import { m } from '$lib/paraglide/messages.js';
 
 /**
@@ -10,9 +10,11 @@ export type DatePrecision = 'DAY' | 'MONTH' | 'SEASON' | 'YEAR' | 'RANGE' | 'APP
 /**
  * Renders a document date at exactly the precision the data claims — never finer.
  *
- * Delegates to the {@link formatDate}/{@link formatMCDate} helpers (so the
- * `T12:00:00` UTC-safety convention and the German Intl formatting are shared,
- * not reimplemented) and routes every localized word through Paraglide.
+ * Every structured part (month name, day-of-month text, season word, prefixes)
+ * is rendered in the active `locale` — DAY, MONTH and RANGE all go through
+ * `Intl.DateTimeFormat(locale, …)` and the localized words through Paraglide —
+ * so an `en`/`es` reader never sees a German month name. The `T12:00:00`
+ * UTC-safety convention is kept via {@link noon}.
  *
  * The label is the SINGLE SOURCE OF TRUTH shared with the Java
  * {@code DocumentTitleFormatter}: both are asserted against
@@ -42,7 +44,7 @@ export function formatDocumentDate(
 
 	switch (precision) {
 		case 'DAY':
-			return formatDate(iso, 'long');
+			return longDate(iso, locale);
 		case 'MONTH':
 			return monthYear(iso, locale);
 		case 'SEASON':
@@ -60,6 +62,14 @@ export function formatDocumentDate(
 
 // ─── precision branches ──────────────────────────────────────────────────────
 
+function longDate(iso: string, locale: string): string {
+	return new Intl.DateTimeFormat(locale, {
+		day: 'numeric',
+		month: 'long',
+		year: 'numeric'
+	}).format(noon(iso));
+}
+
 function monthYear(iso: string, locale: string): string {
 	return new Intl.DateTimeFormat(locale, { month: 'long', year: 'numeric' }).format(noon(iso));
 }