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/views/Mesh.vue

@@ -13,6 +13,7 @@ import MeshDevicePanel from '@/views/mesh/MeshDevicePanel.vue'
 import MeshAssistantPanel from '@/views/mesh/MeshAssistantPanel.vue'
 import HopVizModal from '@/views/mesh/HopVizModal.vue'
 import { rpcClient } from '@/api/rpc-client'
+import { appConfirm } from '@/composables/useAppConfirm'
 import { wsClient } from '@/api/websocket'
 import { IMAGE_COMPRESSION_PRESETS, compressImage, makeThumbnail, type ImageCompressionPreset } from '@/utils/imageCompression'
 import MediaLightbox from '@/components/cloud/MediaLightbox.vue'
@@ -281,7 +282,13 @@ async function refreshOutboxCount() {
 }
 
 async function clearAllMesh() {
-  if (!window.confirm('Clear all mesh peers, messages, and chat history? This cannot be undone.')) return
+  const ok = await appConfirm({
+    title: 'Clear mesh data',
+    message: 'Clear all mesh peers, messages, and chat history? This cannot be undone.',
+    confirmLabel: 'Clear everything',
+    danger: true,
+  })
+  if (!ok) return
   try {
     await rpcClient.call({ method: 'mesh.clear-all' })
     await mesh.refreshAll()
@@ -1419,7 +1426,13 @@ function clearPendingEdit() {
 }
 async function deleteOwnMessage(msg: MeshMessage) {
   if (msg.direction !== 'sent' || msg.sender_seq == null || !activeChatPeer.value) return
-  if (!window.confirm('Delete this message? Peers already received it — this only marks it as deleted.')) return
+  const ok = await appConfirm({
+    title: 'Delete message',
+    message: 'Delete this message? Peers already received it — this only marks it as deleted.',
+    confirmLabel: 'Delete',
+    danger: true,
+  })
+  if (!ok) return
   try {
     await mesh.deleteMessage(activeChatPeer.value.contact_id, msg.sender_seq)
   } catch (e) {