feat(#248): add admin_tag_merge_target_placeholder and admin_tag_merge_success i18n keys

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

frontend/messages/de.json

@@ -598,6 +598,8 @@
 	"admin_tag_merge_confirm_btn": "Jetzt zusammenführen",
 	"admin_tag_merge_step1": "Schritt 1 von 2",
 	"admin_tag_merge_step2": "Schritt 2 von 2",
+	"admin_tag_merge_target_placeholder": "Ziel-Schlagwort suchen …",
+	"admin_tag_merge_success": "Erfolgreich zusammengeführt.",
 	"admin_tag_delete_impact": "{docs} Dokument(e) · {descendants} Untergeordnete",
 	"admin_tag_delete_only_this": "Nur dieses Schlagwort löschen",
 	"admin_tag_delete_only_this_sub": "Untergeordnete werden zu {parent} verschoben",

frontend/messages/en.json

@@ -598,6 +598,8 @@
 	"admin_tag_merge_confirm_btn": "Merge now",
 	"admin_tag_merge_step1": "Step 1 of 2",
 	"admin_tag_merge_step2": "Step 2 of 2",
+	"admin_tag_merge_target_placeholder": "Search target tag …",
+	"admin_tag_merge_success": "Merged successfully.",
 	"admin_tag_delete_impact": "{docs} document(s) · {descendants} child tags",
 	"admin_tag_delete_only_this": "Delete only this tag",
 	"admin_tag_delete_only_this_sub": "Children will be moved to {parent}",

frontend/messages/es.json

@@ -598,6 +598,8 @@
 	"admin_tag_merge_confirm_btn": "Fusionar ahora",
 	"admin_tag_merge_step1": "Paso 1 de 2",
 	"admin_tag_merge_step2": "Paso 2 de 2",
+	"admin_tag_merge_target_placeholder": "Buscar etiqueta de destino …",
+	"admin_tag_merge_success": "Fusionado con éxito.",
 	"admin_tag_delete_impact": "{docs} documento(s) · {descendants} subordinados",
 	"admin_tag_delete_only_this": "Eliminar solo esta etiqueta",
 	"admin_tag_delete_only_this_sub": "Las subordinadas se moverán a {parent}",