fix(mp): 存储层语义统一 + UTF-16 截断修复

- secureGet: 增加 TextEncoder/TextDecoder 替代 charCodeAt 避免 UTF-16 截断
- secureGet: _es_ 前缀键返回空时增加明文键 fallback（对齐 storageGet 语义）
- request.ts safeGet / auth.ts storageGet: 简化为直接委托 secureGet

apps/miniprogram/src/stores/auth.ts

@@ -4,11 +4,9 @@ import * as authApi from '@/services/auth';
 import { secureGet, secureSet, secureRemove } from '@/utils/secure-storage';
 import { clearRequestCache, markLoggingOut, clearLoggingOut, setCachedPatientId } from '@/services/request';
 
-// secureGet fallback: _es_ 加密键为空时尝试明文键（兼容 MCP 注入等场景）
+// secureGet 已内置明文键 fallback，无需再手动 fallback
 function storageGet(key: string): string {
-  const val = secureGet(key);
-  if (val) return val;
-  return Taro.getStorageSync(key) || '';
+  return secureGet(key);
 }
 import { resetAllStores } from './index';