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/assets/styles/style.less

@@ -607,3 +607,50 @@ input:focus-visible {
   width: 100%;
   height: 40vh
 }
+
+// Floating "island" bottom sheet: an ant Drawer (placement="bottom") that
+// sits inset from the screen edges with rounded corners all round, instead
+// of a full-width sheet glued to the bottom. Add `island-sheet` to the
+// Drawer's class. Global because the drawer is teleported to <body>, out of
+// reach of a view's scoped styles.
+.ant-drawer-bottom.island-sheet {
+  --island-gap: 12px;
+
+  .ant-drawer-content-wrapper {
+    left: var(--island-gap);
+    right: var(--island-gap);
+    bottom: calc(var(--island-gap) + env(safe-area-inset-bottom, 0px));
+    width: auto !important;
+    max-width: 480px;
+    margin: 0 auto;
+    border-radius: 26px;
+  }
+
+  // Closed, ant parks the sheet at translateY(100%) inline — that would
+  // leave the gap's worth of sheet peeking up, so push it fully off-screen.
+  &:not(.ant-drawer-open) .ant-drawer-content-wrapper {
+    transform: translateY(calc(100% + var(--island-gap) + 40px + env(safe-area-inset-bottom, 0px))) !important;
+  }
+
+  &.ant-drawer-open .ant-drawer-content-wrapper {
+    box-shadow:
+      0 24px 48px -18px rgba(20, 22, 26, 0.35),
+      0 2px 8px rgba(20, 22, 26, 0.08) !important;
+  }
+
+  .ant-drawer-content {
+    border-radius: inherit;
+    overflow: hidden;
+  }
+
+  // Grab handle, so it still reads as a sheet that can be pulled down.
+  .ant-drawer-body::before {
+    content: '';
+    display: block;
+    width: 38px;
+    height: 4px;
+    margin: 10px auto 0;
+    border-radius: 4px;
+    background: @hairline;
+  }
+}