feat(ui): replace native confirm() with DaisyUI modal composable (F7.2)

Create useConfirm composable (promise-based, singleton state) and
ConfirmModal component. Replace all 10 confirm()/window.confirm() calls
across 9 pages and 1 composable.

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

app/pages/machines/index.vue

@@ -202,10 +202,12 @@ const editMachine = (machine) => {
   navigateTo(`/machine/${machine.id}?edit=true`)
 }
 
+const { confirm: confirmDialog } = useConfirm()
+
 const confirmDeleteMachine = async (machine) => {
   const { showError, showSuccess } = toast
 
-  if (confirm(`Êtes-vous sûr de vouloir supprimer la machine "${machine.name}" ? Cette action est irréversible.`)) {
+  if (await confirmDialog({ message: `Êtes-vous sûr de vouloir supprimer la machine "${machine.name}" ? Cette action est irréversible.` })) {
     try {
       const result = await deleteMachine(machine.id)
       if (result.success) {