feat(document): surface end-before-start inline on the date form (#678)

Add an endBeforeStart $derived to WhoWhenSection (lexicographic ISO compare,
no Date object) that renders an inline error on the end-date field —
border-red-400, aria-invalid, aria-describedby, and a #end-date-error <p>
inside the existing aria-live region — with a ⚠ glyph so the cue is not
colour-alone (WCAG 1.4.1). Save is not disabled; the server stays the gate.

Wire ErrorCode INVALID_DATE_RANGE through errors.ts getErrorMessage and add
the single key error_invalid_date_range to de/en/es, so the same translated
string is used inline (client) and via getErrorMessage (server fallback).

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

frontend/messages/de.json

@@ -655,6 +655,7 @@
 	"person_alias_btn_delete": "Entfernen",
 	"error_alias_not_found": "Der Namensalias wurde nicht gefunden.",
 	"error_invalid_person_type": "Der angegebene Personentyp ist ungültig.",
+	"error_invalid_date_range": "Das Enddatum darf nicht vor dem Startdatum liegen.",
 	"validation_last_name_required": "Nachname ist Pflichtfeld.",
 	"validation_first_name_required": "Vorname ist Pflichtfeld.",
 	"error_ocr_service_unavailable": "Der OCR-Dienst ist nicht verfügbar.",

frontend/messages/en.json

@@ -655,6 +655,7 @@
 	"person_alias_btn_delete": "Remove",
 	"error_alias_not_found": "The name alias was not found.",
 	"error_invalid_person_type": "The specified person type is not valid.",
+	"error_invalid_date_range": "The end date must not be before the start date.",
 	"validation_last_name_required": "Last name is required.",
 	"validation_first_name_required": "First name is required.",
 	"error_ocr_service_unavailable": "The OCR service is not available.",

frontend/messages/es.json

@@ -655,6 +655,7 @@
 	"person_alias_btn_delete": "Eliminar",
 	"error_alias_not_found": "No se encontro el alias de nombre.",
 	"error_invalid_person_type": "El tipo de persona especificado no es válido.",
+	"error_invalid_date_range": "La fecha final no puede ser anterior a la inicial.",
 	"validation_last_name_required": "El apellido es obligatorio.",
 	"validation_first_name_required": "El nombre es obligatorio.",
 	"error_ocr_service_unavailable": "El servicio OCR no está disponible.",