refactor: 优化跨标签会话同步、引入强类型安全JSON解析工具及Seller样式重构

frontend/src/utils/json.ts

@@ -0,0 +1,8 @@
+export function safeParseJSON<T>(raw: string, fallback: T): T {
+  if (!raw || !raw.trim()) return fallback
+  try {
+    return JSON.parse(raw) as T
+  } catch {
+    return fallback
+  }
+}