fix: 修复应用长时间挂后台后恢复时表格数据永久加载的问题

三层防护：
- MySQL 连接获取时执行 ping 健康检查，死连接自动重连
- macOS Reopen 事件 + 前端 visibilitychange 触发连接刷新
- 前端 Promise.race 超时保护，确保 loading 状态不会超过 60s

apps/desktop/src/composables/useVisibilityChange.ts

@@ -0,0 +1,32 @@
+import { onMounted, onUnmounted } from "vue";
+import { refreshConnections } from "@/lib/api";
+import { useQueryStore } from "@/stores/queryStore";
+
+let hiddenAt: number | null = null;
+
+function handleVisibilityChange() {
+  if (document.hidden) {
+    hiddenAt = Date.now();
+  } else {
+    const wasHidden = hiddenAt;
+    hiddenAt = null;
+    if (wasHidden && Date.now() - wasHidden > 30_000) {
+      refreshConnections().catch(() => {});
+      const queryStore = useQueryStore();
+      const stuckTabs = queryStore.tabs.filter((t) => t.isExecuting);
+      if (stuckTabs.length > 0) {
+        queryStore.notifyConnectionMayBeLost();
+      }
+    }
+  }
+}
+
+export function useVisibilityChange() {
+  onMounted(() => {
+    document.addEventListener("visibilitychange", handleVisibilityChange);
+  });
+
+  onUnmounted(() => {
+    document.removeEventListener("visibilitychange", handleVisibilityChange);
+  });
+}