chore(i18n): drop the unused date_original_label key and stale comments

With the visible "Originaltext" line gone from every view, the
date_original_label message has no remaining references — remove it from
de/en/es. Also drop the now-inaccurate comments in documentDate.ts that
described the raw cell as "preserved separately as the visible secondary
line"; the raw cell now only feeds the SEASON word and is never shown.

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

frontend/messages/de.json

@@ -302,7 +302,6 @@
 	"date_season_summer": "Sommer",
 	"date_season_autumn": "Herbst",
 	"date_season_winter": "Winter",
-	"date_original_label": "Originaltext:",
 	"date_unknown_icon_label": "Datum unbekannt",
 	"form_label_date_precision": "Datumsgenauigkeit",
 	"form_label_date_end": "Enddatum",

frontend/messages/en.json

@@ -302,7 +302,6 @@
 	"date_season_summer": "Summer",
 	"date_season_autumn": "Autumn",
 	"date_season_winter": "Winter",
-	"date_original_label": "Original:",
 	"date_unknown_icon_label": "Date unknown",
 	"form_label_date_precision": "Date precision",
 	"form_label_date_end": "End date",

frontend/messages/es.json

@@ -302,7 +302,6 @@
 	"date_season_summer": "Verano",
 	"date_season_autumn": "Otoño",
 	"date_season_winter": "Invierno",
-	"date_original_label": "Texto original:",
 	"date_unknown_icon_label": "Fecha desconocida",
 	"form_label_date_precision": "Precisión de la fecha",
 	"form_label_date_end": "Fecha final",

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

@@ -20,8 +20,7 @@ export type DatePrecision = 'DAY' | 'MONTH' | 'SEASON' | 'YEAR' | 'RANGE' | 'APP
  * {@code DocumentTitleFormatter}: both are asserted against
  * `docs/date-label-fixtures.json` so they cannot drift. The untrusted `raw`
  * cell is only used to derive a season word (a known German season token) — it
- * is otherwise rendered separately by the caller via Svelte default escaping,
- * never interpolated into HTML here.
+ * is never displayed and never interpolated into HTML here.
  *
  * @param iso the sort/filter anchor day (`YYYY-MM-DD`), nullable for UNKNOWN rows
  * @param precision descriptive precision metadata
@@ -82,8 +81,7 @@ function seasonLabel(
 ): string {
 	const month = Number(iso.slice(5, 7));
 	// Prefer the season named in the raw cell; fall back to deriving it from the
-	// anchor month. Either way the WORD is localized (Decision 4) — the verbatim
-	// German raw cell is preserved separately as the visible secondary line.
+	// anchor month. Either way the WORD is localized (Decision 4).
 	const season = seasonFromRaw(raw) ?? seasonOfMonth(month);
 	return `${seasonWord(season, locale)} ${year}`;
 }