feat(前端): 实现Seed抓取的异步交互与提示功能

- 将链接按钮改为带加载状态的交互按钮
- 添加异步请求逻辑，包含防抖和加载指示
- 实现三种状态的Toast提示（成功/无新增/错误）
- 添加相关CSS样式和交互逻辑

public/styles.css

@@ -609,3 +609,43 @@ html, body {
     padding: 12px 16px;
   }
 }
+
+/* Toast (Bottom Right, Non-modal) */
+.toast-br {
+  position: fixed;
+  bottom: 24px;
+  right: 24px;
+  transform: translateY(0);
+  background: rgba(0,0,0,0.8);
+  color: #fff;
+  padding: 10px 16px;
+  border-radius: 20px;
+  font-size: 13px;
+  box-shadow: var(--shadow-md);
+  opacity: 0;
+  transition: all 0.3s ease;
+  pointer-events: none;
+  z-index: 2000;
+  backdrop-filter: blur(10px);
+}
+.toast-br.show {
+  opacity: 1;
+}
+
+/* Button inner loading spinner (shown when .btn has .is-loading) */
+.btn-spinner {
+  width: 16px;
+  height: 16px;
+  border: 2px solid var(--border);
+  border-top-color: var(--accent);
+  border-radius: 50%;
+  animation: spin 0.8s linear infinite;
+  display: none;
+}
+.btn.is-loading .btn-spinner {
+  display: inline-block;
+}
+.btn.is-loading {
+  opacity: 0.9;
+  cursor: not-allowed;
+}