refactor(ui): replace modal dialogs with toast/sheet components

Remove DialogVant/NotifyVant and add Toast and Sheet components with
useToast, useReveal, and usePageTransition composables. Rework
Navigation, RegisterView, and styles across both apps; rebuild dist assets.

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

apps/user-app-v2/src/composables/useToast.ts

@@ -0,0 +1,72 @@
+import { reactive } from 'vue'
+
+/**
+ * App-wide toasts. One shared queue, rendered by <ToastHost> (mounted once in
+ * App.vue), so any view or store can call `toast.success(...)` without placing
+ * a component in its own template.
+ */
+
+export type ToastType = 'success' | 'error' | 'info' | 'warning'
+
+export interface ToastOptions {
+  title?: string
+  /** ms before it closes by itself; 0 keeps it until the user dismisses it. */
+  duration?: number
+  /** Custom icon name; defaults to one per type. */
+  icon?: string
+}
+
+export interface ToastItem {
+  id: number
+  type: ToastType
+  message: string
+  title?: string
+  icon: string
+  duration: number
+}
+
+const DEFAULT_DURATION = 3200
+// Older toasts beyond this are dropped so the stack never covers the screen.
+const MAX_VISIBLE = 3
+
+const ICONS: Record<ToastType, string> = {
+  success: 'vuesax-linear:tick-circle',
+  error: 'vuesax-linear:close-circle',
+  info: 'vuesax-linear:info-circle',
+  warning: 'vuesax-linear:warning-2',
+}
+
+const state = reactive<{ items: ToastItem[] }>({ items: [] })
+let nextId = 1
+
+function show(type: ToastType, message: string, options: ToastOptions = {}): number {
+  const id = nextId++
+  state.items.push({
+    id,
+    type,
+    message,
+    title: options.title,
+    icon: options.icon ?? ICONS[type],
+    duration: options.duration ?? DEFAULT_DURATION,
+  })
+  if (state.items.length > MAX_VISIBLE) state.items.splice(0, state.items.length - MAX_VISIBLE)
+  return id
+}
+
+function dismiss(id: number) {
+  const i = state.items.findIndex((t) => t.id === id)
+  if (i !== -1) state.items.splice(i, 1)
+}
+
+export const toast = {
+  show,
+  dismiss,
+  success: (message: string, options?: ToastOptions) => show('success', message, options),
+  error: (message: string, options?: ToastOptions) => show('error', message, options),
+  info: (message: string, options?: ToastOptions) => show('info', message, options),
+  warning: (message: string, options?: ToastOptions) => show('warning', message, options),
+}
+
+export function useToast() {
+  return { toasts: state.items, ...toast }
+}