fix(ui): replace native confirm() dialogs with the global in-app modal

window.confirm blocks the JS event loop, which froze companion remote
input while open — the remote user could raise the mesh "Clear" prompt
(or reboot / backup-delete / uninstall confirms) and then never dismiss
it, because the synthetic events that would dismiss it queue behind the
dialog itself.

New promise-based appConfirm() (useAppConfirm.ts) + one AppConfirmModal
mounted globally in App.vue, built on BaseModal (Teleport-to-body,
full-viewport backdrop, glass card — the canonical modal contract). All
six native confirm() call sites migrated: mesh clear-all, mesh message
delete, dashboard reboot, backup delete, backup USB copy, app uninstall.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

neode-ui/src/components/AppConfirmModal.vue

@@ -0,0 +1,37 @@
+<template>
+  <BaseModal
+    :show="!!state"
+    :title="state?.title || 'Are you sure?'"
+    z-index="z-[4000]"
+    @close="resolveConfirm(false)"
+  >
+    <p class="text-white/80 text-sm whitespace-pre-line">{{ state?.message }}</p>
+    <template #footer>
+      <div class="flex gap-2">
+        <button
+          type="button"
+          class="flex-1 rounded-lg bg-white/10 hover:bg-white/20 text-white text-sm font-medium py-2.5 transition-colors"
+          @click="resolveConfirm(false)"
+        >
+          {{ state?.cancelLabel || t('common.cancel') }}
+        </button>
+        <button
+          type="button"
+          class="flex-1 glass-button rounded-lg text-sm font-semibold py-2.5"
+          :class="state?.danger ? 'text-orange-400 border-orange-400/30' : ''"
+          @click="resolveConfirm(true)"
+        >
+          {{ state?.confirmLabel || 'Confirm' }}
+        </button>
+      </div>
+    </template>
+  </BaseModal>
+</template>
+
+<script setup lang="ts">
+import { useI18n } from 'vue-i18n'
+import BaseModal from '@/components/BaseModal.vue'
+import { confirmState as state, resolveConfirm } from '@/composables/useAppConfirm'
+
+const { t } = useI18n()
+</script>