refactor(ui): Rediseño completo de UI con Nuxt UI 4

- Nuevo layout responsivo mobile-first con tabs inferiores
- Sidebar colapsable en desktop con cola de impresión
- Sistema de templates reutilizables con localStorage
- Soporte Dark/Light mode con UColorModeButton
- Composables usePrintQueue y useTemplates para estado global
- Componentes modulares: CommandBuilder, QuickActions, PrintQueue, QueueItem
- Navegación por tabs: Constructor | Cola | Templates

app/composables/usePrintQueue.ts

@@ -0,0 +1,81 @@
+export interface Operation {
+  op: string
+  [key: string]: any
+}
+
+export interface PrintResult {
+  ok: boolean
+  msg?: string
+  error?: string
+  code?: string
+  raw?: string
+}
+
+export function usePrintQueue() {
+  const operations = useState<Operation[]>('printQueue', () => [])
+  const result = useState<PrintResult>('printResult', () => ({ ok: true, msg: 'Listo.' }))
+  const loading = useState('printLoading', () => false)
+
+  function addOperations(ops: Operation[]) {
+    if (Array.isArray(ops) && ops.length) {
+      operations.value = [...operations.value, ...ops]
+    }
+  }
+
+  function updateOperation(index: number, op: Operation) {
+    operations.value = operations.value.map((o, i) => i === index ? op : o)
+  }
+
+  function removeOperation(index: number) {
+    operations.value = operations.value.filter((_, i) => i !== index)
+  }
+
+  function moveOperation(from: number, direction: 'up' | 'down') {
+    const to = direction === 'up' ? from - 1 : from + 1
+    if (to < 0 || to >= operations.value.length) return
+
+    const arr = [...operations.value]
+    ;[arr[from], arr[to]] = [arr[to], arr[from]]
+    operations.value = arr
+  }
+
+  function clearQueue() {
+    operations.value = []
+  }
+
+  function loadFromTemplate(ops: Operation[]) {
+    operations.value = JSON.parse(JSON.stringify(ops))
+  }
+
+  async function sendToPrinter() {
+    if (operations.value.length === 0) return
+
+    loading.value = true
+    try {
+      result.value = await $fetch('/api/print', {
+        method: 'POST',
+        body: { operations: operations.value }
+      })
+    } catch (error: any) {
+      result.value = {
+        ok: false,
+        error: error.message || 'Error al enviar a la impresora'
+      }
+    } finally {
+      loading.value = false
+    }
+  }
+
+  return {
+    operations: readonly(operations),
+    result: readonly(result),
+    loading: readonly(loading),
+    addOperations,
+    updateOperation,
+    removeOperation,
+    moveOperation,
+    clearQueue,
+    loadFromTemplate,
+    sendToPrinter
+  }
+}