fix(persons): label rename fields with dedicated first/last-name keys

The triage rename form reused persons_filter_type_person ("Person") and
persons_section_details ("Angaben zur Person") as the first/last-name field
labels, so a screen reader announced the wrong name for each input. Add
dedicated persons_field_first_name / persons_field_last_name keys (de/en/es)
and use them.

Refs #667

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

frontend/messages/de.json

@@ -153,6 +153,8 @@
 	"persons_review_delete_confirm_text": "Diese Person wird endgültig gelöscht. Dokumentverweise bleiben erhalten, verlieren aber diese Person.",
 	"persons_review_delete_confirm_button": "Person löschen",
 	"persons_review_merge_label": "Mit welcher Person zusammenführen?",
+	"persons_field_first_name": "Vorname",
+	"persons_field_last_name": "Nachname",
 	"persons_new_heading": "Neue Person",
 	"persons_section_details": "Angaben zur Person",
 	"person_edit_heading": "Person bearbeiten",

frontend/messages/en.json

@@ -153,6 +153,8 @@
 	"persons_review_delete_confirm_text": "This person will be permanently deleted. Document references are kept but lose this person.",
 	"persons_review_delete_confirm_button": "Delete person",
 	"persons_review_merge_label": "Merge into which person?",
+	"persons_field_first_name": "First name",
+	"persons_field_last_name": "Last name",
 	"persons_new_heading": "New person",
 	"persons_section_details": "Person details",
 	"person_edit_heading": "Edit person",

frontend/messages/es.json

@@ -153,6 +153,8 @@
 	"persons_review_delete_confirm_text": "Esta persona se eliminará de forma permanente. Las referencias de documentos se conservan pero pierden a esta persona.",
 	"persons_review_delete_confirm_button": "Eliminar persona",
 	"persons_review_merge_label": "¿Fusionar con qué persona?",
+	"persons_field_first_name": "Nombre",
+	"persons_field_last_name": "Apellido",
 	"persons_new_heading": "Nueva persona",
 	"persons_section_details": "Datos de la persona",
 	"person_edit_heading": "Editar persona",

frontend/src/lib/person/PersonReviewRow.svelte

@@ -99,7 +99,7 @@ const deleteBtn =
 			<input type="hidden" name="id" value={person.id} />
 			<input type="hidden" name="personType" value={person.personType ?? 'PERSON'} />
 			<label class="flex flex-col gap-1 text-sm">
-				<span class="font-sans text-ink-2">{m.persons_filter_type_person()}</span>
+				<span class="font-sans text-ink-2">{m.persons_field_first_name()}</span>
 				<input
 					name="firstName"
 					bind:value={renameFirstName}
@@ -107,7 +107,7 @@ const deleteBtn =
 				/>
 			</label>
 			<label class="flex flex-1 flex-col gap-1 text-sm">
-				<span class="font-sans text-ink-2">{m.persons_section_details()}</span>
+				<span class="font-sans text-ink-2">{m.persons_field_last_name()}</span>
 				<input
 					name="lastName"
 					required