fix(i18n): use CLDR plural rules in all locale files

Updated cluster-selected in all locales to use proper Fluent CLDR
plural selection instead of hardcoded plural form:
- en, es, it, fr, de: [one] / *[other]
- ru: [one] / [few] / *[many] (verified by unit test)

locales/de/main.ftl

@@ -1,7 +1,10 @@
 cluster-not-found = Cluster "{ $name }" nicht gefunden
 nccl-config-missing = NCCL-Konfiguration nicht gefunden
 cluster-auto-fail = Kein geeigneter Cluster auswählbar
-cluster-selected = ✅ Cluster automatisch ausgewählt: { $name } ({ $nodes } Knoten)
+cluster-selected = ✅ Cluster automatisch ausgewählt: { $name } ({ $nodes } { $nodes ->
+        [one] Knoten
+       *[other] Knoten
+    })
 container-log-header = 📜 Letzte Container-Logs:
 cluster-stopping = 🛑 Cluster '{ $name }' wird gestoppt...
 cluster-all-stopped = ✅ Alle Container gestoppt.

locales/en/main.ftl

@@ -1,7 +1,10 @@
 cluster-not-found = Cluster "{ $name }" not found
 nccl-config-missing = NCCL config not found
 cluster-auto-fail = No suitable cluster found
-cluster-selected = ✅ Auto-selected cluster: { $name } ({ $nodes } nodes)
+cluster-selected = ✅ Auto-selected cluster: { $name } ({ $nodes } { $nodes ->
+        [one] node
+       *[other] nodes
+    })
 container-log-header = 📜 Latest container logs:
 cluster-stopping = 🛑 Stopping cluster '{ $name }'...
 cluster-all-stopped = ✅ All containers stopped.

locales/es/main.ftl

@@ -1,7 +1,10 @@
 cluster-not-found = Clúster "{ $name }" no encontrado
 nccl-config-missing = Configuración NCCL no encontrada
 cluster-auto-fail = No se pudo seleccionar un clúster adecuado
-cluster-selected = ✅ Clúster seleccionado automáticamente: { $name } ({ $nodes } nodos)
+cluster-selected = ✅ Clúster seleccionado automáticamente: { $name } ({ $nodes } { $nodes ->
+        [one] nodo
+       *[other] nodos
+    })
 container-log-header = 📜 Últimos registros del contenedor:
 cluster-stopping = 🛑 Deteniendo el clúster '{ $name }'...
 cluster-all-stopped = ✅ Todos los contenedores detenidos.

locales/fr/main.ftl

@@ -1,7 +1,10 @@
 cluster-not-found = Cluster "{ $name }" introuvable
 nccl-config-missing = Configuration NCCL introuvable
 cluster-auto-fail = Impossible de sélectionner un cluster approprié
-cluster-selected = ✅ Cluster sélectionné automatiquement : { $name } ({ $nodes } nœuds)
+cluster-selected = ✅ Cluster sélectionné automatiquement : { $name } ({ $nodes } { $nodes ->
+        [one] nœud
+       *[other] nœuds
+    })
 container-log-header = 📜 Dernières journaux du conteneur :
 cluster-stopping = 🛑 Arrêt du cluster '{ $name }'...
 cluster-all-stopped = ✅ Tous les conteneurs arrêtés.

locales/it/main.ftl

@@ -1,7 +1,10 @@
 cluster-not-found = Cluster "{ $name }" non trovato
 nccl-config-missing = Configurazione NCCL non trovata
 cluster-auto-fail = Impossibile selezionare un cluster adatto
-cluster-selected = ✅ Cluster selezionato automaticamente: { $name } ({ $nodes } nodi)
+cluster-selected = ✅ Cluster selezionato automaticamente: { $name } ({ $nodes } { $nodes ->
+        [one] nodo
+       *[other] nodi
+    })
 container-log-header = 📜 Ultimi log del contenitore:
 cluster-stopping = 🛑 Arresto del cluster '{ $name }'...
 cluster-all-stopped = ✅ Tutti i contenitori arrestati.