feat: export TelemetryStatus from the package root

client.telemetry_status exists so downstream can reconcile telemetry
programmatically, but annotating its return type meant reaching into
polygateway.types while the convention here is that the top-level
exports are the public API surface. The port itself stays unexported:
nobody outside the library implements it.

tests/unit/test_package.py

@@ -37,3 +37,15 @@ def test_telemetry_schema_sql_exported():
     assert callable(polygateway.telemetry_schema_sql)
     assert "missing_columns_warning" not in polygateway.__all__
     assert not hasattr(polygateway, "missing_columns_warning")
+
+
+def test_telemetry_status_exported():
+    """issue #15: `client.telemetry_status` 的返回类型必须能从顶层 import。
+
+    下游对账/告警要给这个快照做类型标注,若只在 `polygateway.types` 里,标注就得
+    深入子模块,而本库的约定是「顶层导出即公共 API 面」。`TelemetryStatusProvider`
+    则**不**导出: 它是端口,库外无实现者,导出即多一份永久承诺。
+    """
+    assert "TelemetryStatus" in polygateway.__all__
+    assert polygateway.TelemetryStatus is not None
+    assert "TelemetryStatusProvider" not in polygateway.__all__