refactor: split project into web and server directories

- Move frontend to web/ directory
- Add server/ directory for backend
- Restructure project for前后端分离架构

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

web/src/components/shared/ToastNotification.vue

@@ -0,0 +1,31 @@
+<template>
+  <Transition name="toast">
+    <div v-if="toastText" class="toast" role="status" aria-live="polite">{{ toastText }}</div>
+  </Transition>
+</template>
+
+<script setup>
+defineProps({
+  toastText: String
+})
+</script>
+
+<style scoped>
+.toast {
+  position: fixed;
+  right: 22px;
+  bottom: 22px;
+  max-width: min(380px, calc(100vw - 44px));
+  padding: 14px 16px;
+  border-radius: 12px;
+  background: #0b1220;
+  color: #fff;
+  box-shadow: 0 18px 48px rgba(16,24,40,.16);
+  z-index: 120;
+  animation: fadeUp 180ms var(--ease) both;
+}
+.toast-enter-active { transition: opacity 180ms var(--ease), transform 180ms var(--ease); }
+.toast-leave-active { transition: opacity 160ms var(--ease), transform 160ms var(--ease); }
+.toast-enter-from { opacity: 0; transform: translateY(10px); }
+.toast-leave-to { opacity: 0; transform: translateY(-6px); }
+</style>