feat(person): ErrorCode.PERSON_RENAME_CONFLICT for optimistic-lock conflicts

Adds the structured error code returned when a rename rolls back because a
referenced transcription block was edited concurrently (OptimisticLockException
on transcription_blocks.version). Mirrors the contract in
frontend src/lib/errors.ts and adds the localised message keys
error_person_rename_conflict in de/en/es so the UI surfaces a retry hint
instead of a generic 500.

The actual translation of OptimisticLockException → DomainException
(PERSON_RENAME_CONFLICT) lands in the next commit alongside the integration
test that proves the rollback semantics.

Refs #362

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

backend/src/main/java/org/raddatz/familienarchiv/exception/ErrorCode.java

@@ -15,6 +15,10 @@ public enum ErrorCode {
     ALIAS_NOT_FOUND,
     /** The submitted personType value is not allowed (e.g. SKIP is import-only). 400 */
     INVALID_PERSON_TYPE,
+    /** A concurrent edit on a referenced transcription block prevented the rename
+     * from committing (optimistic-lock conflict). The whole rename rolls back; the
+     * client should refetch and retry. 409 */
+    PERSON_RENAME_CONFLICT,
 
     // --- Documents ---
     /** A document with the given ID does not exist. 404 */

frontend/messages/de.json

@@ -542,6 +542,7 @@
 	"person_alias_btn_delete": "Entfernen",
 	"error_alias_not_found": "Der Namensalias wurde nicht gefunden.",
 	"error_invalid_person_type": "Der angegebene Personentyp ist ungültig.",
+	"error_person_rename_conflict": "Eine andere Bearbeitung hat einen verknüpften Transkriptionsblock gleichzeitig geändert. Bitte erneut versuchen.",
 	"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

@@ -542,6 +542,7 @@
 	"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_person_rename_conflict": "Another edit modified a referenced transcription block at the same time. Please try again.",
 	"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

@@ -542,6 +542,7 @@
 	"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_person_rename_conflict": "Otra edición modificó un bloque de transcripción referenciado al mismo tiempo. Por favor, inténtalo de nuevo.",
 	"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.",

frontend/src/lib/errors.ts

@@ -8,6 +8,7 @@ export type ErrorCode =
 	| 'PERSON_NOT_FOUND'
 	| 'ALIAS_NOT_FOUND'
 	| 'INVALID_PERSON_TYPE'
+	| 'PERSON_RENAME_CONFLICT'
 	| 'DOCUMENT_NOT_FOUND'
 	| 'DOCUMENT_NO_FILE'
 	| 'FILE_NOT_FOUND'
@@ -79,6 +80,8 @@ export function getErrorMessage(code: ErrorCode | string | undefined): string {
 			return m.error_alias_not_found();
 		case 'INVALID_PERSON_TYPE':
 			return m.error_invalid_person_type();
+		case 'PERSON_RENAME_CONFLICT':
+			return m.error_person_rename_conflict();
 		case 'DOCUMENT_NOT_FOUND':
 			return m.error_document_not_found();
 		case 'DOCUMENT_NO_FILE':