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/composables/useAppConfirm.ts

@@ -0,0 +1,44 @@
+/**
+ * Promise-based in-app replacement for window.confirm(). Native browser
+ * modals block the JS event loop while open, which freezes the companion
+ * remote-input relay (and every other async path) — a remote user could
+ * raise a confirm they can never dismiss, since the synthetic events that
+ * would dismiss it are queued behind the very dialog they need to close.
+ *
+ * State is module-level so the single <AppConfirmModal /> mounted in
+ * App.vue serves every caller:
+ *
+ *   const ok = await appConfirm('Clear everything? This cannot be undone.')
+ *   const ok = await appConfirm({ message: '…', confirmLabel: 'Delete', danger: true })
+ */
+import { ref } from 'vue'
+
+export interface AppConfirmOptions {
+  title?: string
+  message: string
+  confirmLabel?: string
+  cancelLabel?: string
+  /** Styles the confirm button as destructive (orange/warning). */
+  danger?: boolean
+}
+
+interface ActiveConfirm extends AppConfirmOptions {
+  _resolve: (value: boolean) => void
+}
+
+export const confirmState = ref<ActiveConfirm | null>(null)
+
+export function appConfirm(options: AppConfirmOptions | string): Promise<boolean> {
+  const opts = typeof options === 'string' ? { message: options } : options
+  // A second confirm while one is open cancels the first — the browser
+  // primitive this replaces could only ever show one at a time.
+  confirmState.value?._resolve(false)
+  return new Promise<boolean>((resolve) => {
+    confirmState.value = { ...opts, _resolve: resolve }
+  })
+}
+
+export function resolveConfirm(result: boolean) {
+  confirmState.value?._resolve(result)
+  confirmState.value = null
+}