🐛 fix(query-export): 修复查询结果导出卡住并统一按数据源能力控制导出路径

- 查询结果页导出增加稳定兜底，异常时确保 loading 关闭避免持续转圈
- DataGrid 导出逻辑按数据源能力分流，优先走后端 ExportQuery 并保留结果集导出降级
- QueryEditor 传递结果导出 SQL，保证查询结果导出范围与当前结果一致
- 后端补充 ExportData/ExportQuery 关键日志，提升导出链路可观测性

internal/db/optional_driver_agent_impl_test.go

@@ -0,0 +1,32 @@
+package db
+
+import (
+	"context"
+	"testing"
+	"time"
+)
+
+func TestTimeoutMsFromContext_NoDeadline(t *testing.T) {
+	if got := timeoutMsFromContext(context.Background()); got != 0 {
+		t.Fatalf("无 deadline 时应返回 0，got=%d", got)
+	}
+}
+
+func TestTimeoutMsFromContext_WithDeadline(t *testing.T) {
+	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
+	defer cancel()
+
+	got := timeoutMsFromContext(ctx)
+	if got <= 0 {
+		t.Fatalf("有 deadline 时应返回正值，got=%d", got)
+	}
+}
+
+func TestTimeoutMsFromContext_ExpiredDeadline(t *testing.T) {
+	ctx, cancel := context.WithDeadline(context.Background(), time.Now().Add(-time.Second))
+	defer cancel()
+
+	if got := timeoutMsFromContext(ctx); got != 1 {
+		t.Fatalf("过期 deadline 应返回 1，got=%d", got)
+	}
+}