feat: cascade-delete hosts when removing a network

When a VLAN/LAN is deleted, all non-gateway, non-livebox devices
with an interface in that network are deleted automatically.
Gateway and livebox devices are preserved; their interface is
unlinked (vlan_id set to NULL).

The confirmation dialog now shows the exact count of devices
that will be deleted (all three locales: fr/en/es).

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

frontend/src/components/VlanManager.vue

@@ -90,7 +90,7 @@ import { ref, reactive } from 'vue'
 import { vlansApi } from '../api.js'
 import { t, tFmt } from '../i18n.js'
 
-const props = defineProps({ vlans: Array })
+const props = defineProps({ vlans: Array, devices: { type: Array, default: () => [] } })
 const emit = defineEmits(['refresh'])
 
 const showForm = ref(false)
@@ -145,9 +145,18 @@ async function save() {
   }
 }
 
+function _affectedCount(vlan) {
+  return props.devices.filter(
+    d => !d.is_gateway && !d.is_livebox && d.interfaces.some(i => i.vlan_id === vlan.id)
+  ).length
+}
+
 async function remove(vlan) {
   const label = vlan.vlan_id != null ? `VLAN ${vlan.vlan_id} — ${vlan.name}` : `LAN ${vlan.name}`
-  if (!confirm(`Supprimer ${tFmt('confirmDeleteNetwork', label)}`)) return
+  const count = _affectedCount(vlan)
+  let msg = `Supprimer ${tFmt('confirmDeleteNetwork', label)}`
+  if (count > 0) msg += '\n' + tFmt('confirmDeleteNetworkHosts', count)
+  if (!confirm(msg)) return
   try {
     await vlansApi.remove(vlan.id)
     emit('refresh')