i18n: pass all visible UI strings through t() — no more hardcoded labels

Move Link, GW, LXC, VM chip tags, WAN labels, form placeholders, and
confirm-dialog delete verbs into i18n.js for all three locales (fr/en/es).
confirmDeleteDevice and confirmDeleteNetwork now include the action verb
so the JS callers no longer hardcode "Supprimer".

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

frontend/src/components/VlanManager.vue

@@ -51,7 +51,7 @@
           </div>
           <div class="field">
             <label>{{ t('fieldName') }}</label>
-            <input v-model="form.name" type="text" required placeholder="ex: Serveurs" />
+            <input v-model="form.name" type="text" required :placeholder="t('networkNamePlaceholder')" />
           </div>
           <div class="field">
             <label>{{ t('subnet') }}</label>
@@ -154,7 +154,7 @@ function _affectedCount(vlan) {
 async function remove(vlan) {
   const label = vlan.vlan_id != null ? `VLAN ${vlan.vlan_id} — ${vlan.name}` : `LAN ${vlan.name}`
   const count = _affectedCount(vlan)
-  let msg = `Supprimer ${tFmt('confirmDeleteNetwork', label)}`
+  let msg = tFmt('confirmDeleteNetwork', label)
   if (count > 0) msg += '\n' + tFmt('confirmDeleteNetworkHosts', count)
   if (!confirm(msg)) return
   try {