i18n(person-mention): add 5 locale keys for editor + read-mode

Adds the 3 keys mandated by the plan (open_link, hover_hint, load_error)
plus the editor's popup_empty + btn_label so PersonMentionEditor mirrors
the existing user-mention editor's i18n pattern.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/messages/de.json

@@ -420,6 +420,11 @@
 	"notification_unread": "ungelesen",
 	"mention_btn_label": "Person erwähnen",
 	"mention_popup_empty": "Keine Nutzer gefunden",
+	"person_mention_open_link": "Zur Person",
+	"person_mention_hover_hint": "Klick öffnet Seite",
+	"person_mention_load_error": "Person konnte nicht geladen werden.",
+	"person_mention_popup_empty": "Keine Personen gefunden",
+	"person_mention_btn_label": "Person verlinken",
 	"page_title_home": "Archiv",
 	"page_title_persons": "Personen",
 	"page_title_admin": "Administration",

frontend/messages/en.json

@@ -420,6 +420,11 @@
 	"notification_unread": "unread",
 	"mention_btn_label": "Mention person",
 	"mention_popup_empty": "No users found",
+	"person_mention_open_link": "Open person",
+	"person_mention_hover_hint": "Click opens the page",
+	"person_mention_load_error": "Could not load person.",
+	"person_mention_popup_empty": "No persons found",
+	"person_mention_btn_label": "Link person",
 	"page_title_home": "Archive",
 	"page_title_persons": "Persons",
 	"page_title_admin": "Administration",

frontend/messages/es.json

@@ -420,6 +420,11 @@
 	"notification_unread": "no leído",
 	"mention_btn_label": "Mencionar persona",
 	"mention_popup_empty": "No se encontraron usuarios",
+	"person_mention_open_link": "Ir a la persona",
+	"person_mention_hover_hint": "Clic abre la página",
+	"person_mention_load_error": "No se pudo cargar la persona.",
+	"person_mention_popup_empty": "No se encontraron personas",
+	"person_mention_btn_label": "Vincular persona",
 	"page_title_home": "Archivo",
 	"page_title_persons": "Personas",
 	"page_title_admin": "Administración",